Method of assembling the oscillating assembly of a surgical sagittal saw

ABSTRACT

A method of assembling a surgical sagittal saw that includes an oscillating head. The oscillating head and the yoke used to drive the head are formed with complementary tapered surfaces. The oscillating head is seated in the yoke so the tapered surfaces are adjacent. The yoke and head are pressed together so the yoke and head tapered surfaces abut. As a result of tapered surfaces abutting the oscillating head and yoke effectively become a single unit. The oscillating head and yoke are mounted to the saw body so the yoke can be driven by the drive shaft integral with the saw. The oscillating head is rotatably mounted to the saw. Thus, upon actuation of the drive shaft, the drive shaft oscillates the yoke so as to foster similar oscillations in the oscillating head. The oscillating head drives the saw blade attached to the saw.

PRIORITY CLAIM

This application is a divisional of U.S. patent application Ser. No.14/134,152 filed 19 Dec. 2013 now U.S. Pat. No. 9,060,783. ApplicationSer. No. 14/134,152 is a divisional of U.S. patent application Ser. No.13/739,110 filed 11 Jan. 2013, now U.S. Pat. No. 8,696,673. ApplicationSer. No. 13/737,110 a divisional of application Ser. No. 12/622,944filed 20 Nov. 2009 now U.S. Pat. No. 8,444,647. Application Ser. No.12/622,944 is a divisional of application Ser. No. 11/504,945 filed 16Aug. 2006, now U.S. Pat. No. 7,704,254. Application Ser. No. 11/504,945claims priority under 35 U.S.C. Sec. 119 from U.S. Pat. App. No.60/715,821 filed 10 Sep. 2005. The contents of the priority applicationsare incorporated herein by reference.

FIELD OF THE INVENTION

This invention is related generally to a surgical saw and, moreparticularly, a surgical sagittal saw and a complementary saw bladeassembly.

BACKGROUND OF THE INVENTION

A sagittal saw is a powered surgical tool that is typically used in anorthopedic surgical procedure. A sagittal saw generally includes ahandpiece that houses a motor and the complementary control circuit thatregulates actuation of the motor. Extending forward, distally, from thehandpiece is a head. Internal to the head is an oscillating shaft.Removably attached to the oscillating shaft is a saw blade. The exposeddistal front edge of the blade is formed with teeth. The teeth cut thetissue against which the blade is applied. A drive mechanism internal tothe housing generates power. This power is applied to actuate theoscillating shaft so that the shaft and the attached blade move in aback-and-forth pattern in which the blade is aligned. When the saw is soactuated, the blade teeth move in a back-and-forth pattern against thetissue against which they are applied. Due to the forward pressureapplied by the surgeon holding the saw, the teeth cut and separate thehard tissue against which the blade is applied.

A sagittal saw is often used in an orthopedic surgical procedure toselectively remove bone. One particular type of orthopedic surgicalprocedure in which the saw is used is a joint replacement procedure. Asimplied by the name, in this type of procedure, the surgeon resects thebone between the joints in the patient and substitutes an artificialjoint.

In an orthopedic surgical procedure it is important to ensure that, whenthe section to be resected is separated from the remaining bone, thesection is removed along precise lines. Accuracy is mandatory becausethe substitute joint typically has a component designed to precisely fitin the space left by the cut line of the bone left in place.

To ensure the cuts are properly formed in the bone, the surgeontypically first mounts a cutting guide, sometimes called a jig, to thebone adjacent the location at which the cut is to be made. One type ofcutting guide is in the form of a block with a precisely shaped set ofslots. The slots define the lines along which the bone is to be cut. Thesurgeon removes the bone by sequentially inserting the saw blade in theslots. Once the blade is inserted in a slot, the saw is actuated. Thisarrangement enables the surgeon to cut the bone along the preciselydefined lines.

Presently available sagittal saws and their complementary bladesadequately cut the bone against which the blades are applied. However,some limitations are associated with these assemblies. Many commerciallyavailable sagittal saws are provided with planar blades that oscillate.The blade inevitably rubs against the cutting guide material thatdefines the slot(s) in which the blade is inserted. This repetitivecontact wears away the slot-defining material. Eventually the slot maybecome so wide that it no longer precisely defines the intended cutline. Once a cutting guide is so worn, it needs to be replaced.

It should similarly be appreciated that, the repeated abutment of thesaw blade against the cutting guide can cause the guide to move. If anaccurate cut is desired this movement is, at a minimum, undesirable.

Moreover, the wearing of the material forming the cutting guidegenerates a fine dust of material. Some of this dust inevitably settleson the surgical site at which the procedure is being performed.Consequently, during the procedure, the surgical personnel are requiredto spend an appreciable amount of time flushing the site to remove thisdust. Having to repeatedly perform this process runs counter to one ofthe primary goals when performing surgery; that one should perform theprocedure as quickly as possible to minimize the time that both theexposed tissue is open to infection and the patient is held underanesthesia.

As discussed above, the oscillating blade of a current surgical saw willrepeatedly gall the surfaces of the cutting guide forming the slot inwhich the blade is inserted. One further disadvantage of this bladegalling it consumes power. Many sagittal saws are battery powered. Thepower expended overcoming the blade galling-induced friction reduces theoverall amount of power available to actuate the saw. This reduces theoverall amount of time the battery, on a single charge, is able to powerthe saw.

Moreover, as a consequence of the saw blade galling against a surface ofthe cutting guide, then pulling away from this surface, there is somejerking of the blade. The jerking motion is transferred from the bladethrough the handpiece into the hand of the surgeon holding the saw.Consequently, the surgeon must exert some muscle control to hold thehandpiece steady when he/she is exposed to this jerking motion.

Also, an inevitable result of the back-and-forth motion of the blade,the sagittal saw invariable vibrates. Again, the surgeon is required toengage in some conscious or unconscious physical effort to hold the sawsteady when it vibrates. Over time, having to so hold the saw toovercome this vibration can be significantly mentally and physicallyfatiguing.

The Applicant's Assignee's U.S. patent application Ser. No. 10/887,642,SURGICAL SAGITTAL SAW AND METHOD OF USING SAME, filed 9 Jul. 2004, U.S.Patent Publication No. 2006/0009796 A1, now U.S. Pat. No. 7,497,860,incorporated herein by reference, discloses a saw and complementary sawblade that are designed to overcome, if not essentially eliminate, thelimitations described above. The blade assembly of this inventionincludes a bar to which a blade head is pivotally mounted. Drive rodsdisposed in the bar extend proximally rearward. The blade bar isremovably attached to a head that is part of that is part of the saw ofthis invention. The drive rods are coupled to an oscillating shaftintegral with saw head. When the saw of this invention is actuated, theoscillating shaft moves back and forth. This movement, in turn, causesthe drive rods to reciprocate. The drive rods thus oscillate the bladehead around the pivot point against which it is mounted.

The above saw and blade assembly are designed so that, only the distallylocated blade head oscillates. The blade assembly bar remains static.This eliminates many of the problems that otherwise occur if the wholeof the blade assembly is allowed to move back and forth.

The assembly of the above application works well. However, this assemblyrelies on removable threaded fasteners to removably hold the bladeassembly to the saw head. Surgical personnel must use a tool to firstremove, and, then, replace the saw blade. Having to perform these stepsin surgery can lengthen the overall time it takes to perform theprocedure. Moreover, this action requires the surgical personnel toaccount for the threaded fasteners as well as the component to whichthey are attached.

Also, debris from cut tissue can enter the bars of some bladeassemblies. These debris can potentially inhibit blade head oscillation.

Furthermore, it is desirable to provide a sagittal saw with an assemblythat allows the saw head to be rotated, indexed, around the longitudinalaxis of the head. This is because often it is desirable to position thehead so that the complementary blade assembly is disposed in a planethat is not simply perpendicular to the axis that extends top-to-bottomthrough the saw. Therefore, this type of saw normally includes anindexing assembly that allows the saw head to be rotated, indexed, to aselect angular orientation and locked in place.

A conventional indexing mechanism typically includes a single biasingmember, a spring, that holds the head in a fixed index orientation.Often, surgical personnel find it difficult to manually overcome theforce imposed by this spring in order to rotate the saw head.

SUMMARY OF THE INVENTION

This invention relates to a new and useful surgical sagittal saw and acomplementary blade assembly designed for use with the saw. The sagittalsaw of this invention has a head with a toolless coupling assembly forreleasably holding the blade assembly in place. The coupling assemblyalso does not include components that are removed from the head. The sawhead is also relatively easy to release from a locked indexed position,rotate to a new index position and then lock in the new index position.The blade assembly of this invention ejects debris that enter the bladebar.

More specifically, the saw of this invention is provided with anassembly that allows the oscillating unit to which the blade drive rodsare attached to move. This minimizes the efforts required to insert andremove the blade assemblies. The coupling assembly clamps the blade barin place. Neither of these assemblies have components that are removedfrom the saw head in order to remove and replace the attached bladeassembly.

Also integral with the saw head is a first biasing member that holds thehead against the saw housing component from which the head extends. Alock assembly prevents the rotation of the saw head. A second biasingmember, part of the lock assembly, latching the locking assembly inposition. Collectively, these sub-assemblies make it relatively easy tounlock, index and relock the saw head in a fixed angular orientation.

The blades assembly of this invention includes both the blade bar and ablade head that is pivotally attached to the bar. Openings are formed inboth the blade bar and blade head. Collectively, these openings arepositioned to form a discharge path through which debris that enter thebar are ejected. This essentially eliminates the possibility thatentrance of such material into the blade bar can adversely affect bladeoperation.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further features and benefits of this invention areunderstood from the Detailed Description below taken in conjunction withthe attached drawings in which:

FIG. 1 is a perspective view of a surgical sagittal saw with saw bladeattached that is constructed in accordance with this invention;

FIG. 2 is a cross sectional view of the motor and saw distal end withattached blade of this invention;

FIG. 3 is an enlarged cross sectional view of the proximal portion ofthe assembly illustrated in FIG. 2;

FIG. 4 is an enlarged cross sectional view of the distal portion of theassembly illustrated in FIG. 2;

FIG. 5 is a cross sectional view of the saw motor housing;

FIG. 6 is a perspective view of the saw head;

FIG. 7 is a side view of the saw head;

FIG. 7A is a top view of the saw head;

FIG. 8 is a cross sectional view of the saw head;

FIG. 9 is a cross sectional view of the inner race of the proximallylocated bearing assembly disposed around the saw head;

FIG. 10 is a cross sectional view of the outer race of the proximallylocated bearing assembly disposed around the saw head

FIG. 11 is a perspective view of the retainer ring fitted to theproximal end of the saw head;

FIG. 12 is a perspective view of the outer race of the distal locatedbearing assembly disposed around the saw head;

FIG. 13 is a cross sectional view of the outer race of FIG. 12;

FIG. 14 is a cross sectional view of the threaded ring that holds themoor housing to the saw;

FIG. 15 is a perspective view of the indexing assembly lock link;

FIG. 16 is a side view of the indexing assembly lock link;

FIG. 17 is an enlarged cross sectional view of illustrating how theindexing lock link holds the saw head in a select orientation;

FIG. 18 is a first plan view of the saw output shaft;

FIG. 19 is a second plan view of the saw output shaft at positiondifferent from that shown in the first plan view;

FIG. 20 is a cross sectional view of the rear inner housing;

FIG. 21 is a cross sectional view of the rotor drive coupler;

FIG. 22 is a top plan view of the front inner housing internal to thesaw head;

FIG. 23 if a front plan view of the front inner housing;

FIG. 24 is a cross sectional view of the front inner housing taken alongline 24-24 of FIG. 22;

FIG. 25 is a perspective view of the oscillating shaft;

FIG. 26 is side plan view of the oscillating shaft;

FIG. 27 is a cross sectional view of the oscillating shaft taken alongline 27-27 of FIG. 26;

FIG. 27A is a cross sectional view of the oscillating shaft taken alongline 27A-27A of FIG. 27.

FIG. 28 is a top view of the oscillating head;

FIG. 29 is a cross sectional view of the oscillating head taken alongline 29-29 of FIG. 29;

FIG. 30 is a cross sectional view of the shaft screw fitted to theoscillating shaft;

FIG. 31 is a perspective view of the wobble ring;

FIG. 32 is a plan view of the wobble ring;

FIG. 33 is a cross sectional view of the wobble ring taken along line32-32 of FIG. 32;

FIG. 34 is a perspective view of the blade coupling rod;

FIG. 35 is a plan view of the blade coupling rod;

FIG. 36 is a perspective view of the wing nut;

FIG. 37 is a cross sectional view of the wing nut;

FIG. 38 is a cross sectional view of the wing nut retainer;

FIG. 39 is a perspective view of the blade coupling assembly cam;

FIG. 40 is a side plan view of the cam;

FIG. 41 is a cross sectional view of the cam;

FIG. 42 is a cross sectional view of the blade coupling assemblydepicting the position of the components when the assembly is in theblade load, unlocked, state;

FIG. 43 is an exploded view of the blade assembly;

FIG. 44 is a cross sectional view of the blade coupling assemblydepicting the position of the components when the assembly in the run,locked, state;

FIG. 45 is an exploded view of an alternative saw head assembly of thisinvention;

FIG. 46 is a cross sectional view of the saw head assembly of claim 45;

FIG. 47 is a perspective view of the saw head of the alternative sawhead assembly;

FIG. 48 is a top view of the alternative saw head;

FIG. 49 is a cross sectional view of the alternative saw head takenalong line 49-49 of FIG. 48;

FIG. 50 is a perspective view of the inner housing of the alternativesaw head;

FIG. 51 is a top view of the alternative inner housing;

FIG. 52 is a cross sectional view of the inner housing taken along line52-52 of FIG. 51;

FIG. 53 is a perspective view of the bearing retainer;

FIG. 54 is a side view of the drive shaft;

FIG. 55 is a perspective view of the bearing retainer;

FIG. 56 is a perspective view of the oscillating yoke;

FIG. 57 is a cross sectional view through the oscillating yoke;

FIG. 58 is an exploded view of the oscillating head and the componentsattached thereto;

FIG. 59 is a cross sectional view of the oscillating head;

FIG. 60 is perspective view of the nut that hold the oscillating yokeand oscillating head together;

FIG. 60A is a cross sectional view of the nut of FIG. 60;

FIG. 61 is a perspective view of the plunger;

FIG. 62 is a side view of the plunger;

FIG. 63 is a perspective view of the plunger retainer;

FIG. 64 is a cross sectional view of the plunger retainer;

FIG. 65 is an exploded view of an alternative blade assembly of thisinvention;

FIG. 66 is a perspective view of another alternative oscillating yoke;

FIG. 67 is a perspective view of the another oscillating head;

FIG. 68 is a perspective view of the oscillating assembly retainingscrew for use with oscillating yoke of FIG. 66 and the oscillating headof FIG. 67;

FIG. 69 is an exploded view of an alternative blade assembly of thisinvention;

FIG. 70 is a cross sectional view of the module internal to the bladeassembly of FIG. 54 that contains an RFID;

FIG. 71 is a cross sectional view of the saw head used with thealternative blade assembly of FIG. 54;

FIG. 72 is a combined schematic and block diagram of the circuit thatreads the data stored in the RFID and that regulates the actuation ofthe saw based on the data;

FIG. 73 is a block diagram representative of the memory of the RFID and,more particularly, the types of data stored in the memory;

FIG. 74 is a flow chart of the process steps executed in order to readthe data in blade assembly RFID;

FIG. 75 is a diagrammatic illustration of how the surgical saw of thisinvention is used with a surgical navigation system;

FIG. 76 is a flow chart of the process steps executed in order to employa surgical navigation system to determine the position of the blade headof a saw blade according to this invention;

FIG. 77 is a plan view of another alternative blade assembly of thisinvention; and

FIG. 78 is a side view of the blade assembly of FIG. 77.

It should be appreciated that the above drawings that illustratemechanical elements of this invention should be understood to generallyshow the relative proportions of the individual features of the elementcomponents and of the elements to each other.

DETAILED DESCRIPTION I. Overview

FIGS. 1 and 2 depict the surgical saw 50 of this invention and the bladeassembly 52 used with the saw. Saw 50 includes a housing 54. The housing54 has an elongated, top-located barrel section 56. A pistol-grip shapedhandle 58, also part of housing 54, extends downwardly from barrelsection 56. A motor 60 is disposed inside the housing barrel section 56.In some versions of the invention, motor 60 is a brushless, sensorlessDC motor. This is exemplary, not limiting. In other versions of theinvention, the motor 60 may be a DC motor with brushes and/or sensors,an AC driven motor or a motor that is pneumatically or hydraulicallydriven. In the illustrated version of the invention, saw 50 is acordless power tool. A battery 62 removably attached to the butt end ofhandle 58 contains a charge for energizing the motor. Again, it shouldbe understood that the invention is not so limited. In alternativeversions of the invention, a power cord, an air line or a fluid line isconnected to the housing 54 for providing the power needed to actuatethe motor 60.

A front plate 64 is fitted over the distal end opening of the housingbarrel section 56. (“Distal”, it shall be understood, means toward thesurgical site to which the handpiece 30 is directed. “Proximal” meansaway from the surgical site.) A trigger 66 is moveably mounted to thefront plate 64 and extends forward of the front plate. A control circuitinternal to the housing handle 58, not illustrated and not part of thisinvention, monitors actuation of the trigger 66. Based on the extent towhich the trigger 66 is actuated, the control circuit selectivelyenergizes motor 60 to cause a motor rotor 98 to rotate at the desiredspeed

A head 68 extends forward from the front plate 64 above the trigger 66.The proximal end of blade assembly 52 is removably fitted to the head68. Internal to the saw head 68 is an oscillating head 70 (FIGS. 2 and28). Oscillating head 70 includes a pair of pins 72. When the bladeassembly 52 is mounted to the saw head 68, drive rods 74 (FIG. 43), partof the blade assembly 52, engage the pins. When the saw motor 60 isactuated, the oscillating head 70 and pins 72 oscillate. The movement ofthe pins 72 causes the drive rods 74 to reciprocate. A blade head 76forms the most distal end of the blade assembly 52. The drive rods 74are attached to the blade head 76. The reciprocal movement of the driverods 74 causes the blade head 76 to oscillate back and forth in acutting motion.

II. Saw Motor, Saw Head and Indexing Assembly

FIGS. 2, 3 and 4 illustrate how motor 60 and saw head 68 are mounted tothe rest of the saw 50, more particularly, the front plate 64. The motor60 includes a tube-like motor housing 80 now described by reference toFIG. 5. The motor housing 80 is formed to have a main section 82 ofconstant diameter that extends distally forward from the proximal rearend of the housing. Main section 82 extends along approximately 80% ofthe length of the housing. Motor housing main section 82 is primarilycylindrical. Nevertheless, the main section 82 is formed to define anotch 83 that extends forward from the main section proximal end. Notch83 functions as void space through which electrical connectors notillustrated and not part of this invention extend to the motor 60.

Forward of main section 82, the motor housing 80 has a first collar 84with a smooth outer wall. Collar 84 has a diameter less than that ofmain section 82. A second collar 86 forms the most distal end of themotor housing 80. Second collar 86 has an outer diameter approximatelyequal to that of first collar 84. The outer surface of the motor housing80 forming the second collar 86 is threaded, (threading notillustrated).

Motor housing 80 is formed to have a first bore 88 that extends distallyforward from the proximal rear end of the housing. The motor housing 80is further formed to define a groove 89 that extends circumferentiallyaround a portion of the proximally located inner wall of the housingthat defines the first bore. More particularly, the groove 89 is formedin the section of the main housing 80 interrupted by notch 83. Extendingcoaxially forward from the first bore 82, the motor housing is formed tohave a second and third bores 90 and 92, respectively. Second bore 90has a diameter less than that of the first bore 88. Third bore 92 has adiameter less than that of the second bore 90. Collectively, bores 88and 90 are located in the housing main section 82. The third bore 92extends from the main section 82 and into the space subtended by thefirst collar 84. A fourth bore 94, coaxial with bores 88, 90 and 92,forms the open distal end of the motor housing 80. Bore 94 extendsthrough the motor housing second collar 86 and partially into the firstcollar 84.

Motor 60 includes a stator is represented in FIG. 3 by a number of wires96 motor cap 110 and part of a lamination stack 97 in the housing firstbore 88. The motor 60 is completed by a rotor 98 that is rotatablyfitted in the housing first bore 88 and that is centered along thelongitudinal axis of the motor housing 80. As seen by FIG. 3, rotor 98is formed to have a proximal end stem 102. Not shown in the Figures isthe bearing assembly that extends between the rotor stem 102 and theadjacent inner wall of the motor housing 80 that defines the first bore88. Also not seen is the snap clip seated in groove 89 holds the bearingassembly and stator 96 in position.

Forward of stem 102, motor rotor 98 has a main section 104 with adiameter larger than that of the stem 102. The rotor main section 104includes the motor magnets, (not explicitly illustrated). Forward of themotor main section 104 there is a neck 106 that has a diameterapproximately equal to that of the stem. A circular head 108 forms thedistalmost, forwardmost section of the rotor 98. Rotor head 108 has anouter diameter less than that of the adjacent neck 106. The rotor 98 isfurther formed with an axially extending bore 109 that extends betweenthe proximal and distal ends of the rotor.

The rotor head 108 is rotatably mounted to a cap 110, seen best in FIG.3, disposed in the distal most portion of the motor housing first bore88. Cap 110 has a sleeve shaped outer skirt 112. A disc-like base 114extends over the forward section of skirt 112. It will be observed thatthe distally directed face of cap base 114 is slightly recessed relativeto the annular front surface of the skirt 112. The cap 110 is furtherformed to have a circumferential flange 116 that extends proximallyrearward around the center of the cap base 114. Flange 116 has anL-shaped cross-sectional profile. The inwardly directed circumferentialedge of flange 116 defines an opening 118 through the cap base 114.

Cap 110 is fit in the distal end base of the motor housing first bore88. The rotor neck 106 extends through the cap opening 118; rotor head108 is seated in the void space defined by the cap circumferentialflange 116. A bearing assembly 120 extends between the rotor head 108and the flange 114 to rotatably couple the rotor 98 to the cap 110.

The saw head 68, now described by reference to FIGS. 6-8, is formed froma single piece of metal. The saw head 68 is formed to define acylindrically shaped proximal end section 124. More specifically,proximal end section 124 has an outer diameter dimensioned to allow thesection to freely rotate when fitted in the motor housing third bore 92.Forward of the proximal end section 124, there is a cylindrical firstintermediate section 128. First intermediate section 128 has an outerdiameter greater than that of the proximal end section and less thanthat of the motor housing fourth bore 94. Saw head 68 is formed so thatbetween the proximal end section 124 and the first intermediate section128 there is tapered surface 126. Saw head first intermediate section128 is further shaped to define two rectangularly shaped, diametricallyopposed through openings 130 into the center of the saw head 68.

A second intermediate section 132, also having a cylindricalcross-sectional profile, extends distally forward from the firstintermediate section 128. Second intermediate section 132 has a diametergreater than that of the first intermediate section 128. The secondintermediate section 132 is formed with a circular bore 133. Bore 133 ispositioned so that center of the opening is located on a line that is anextension of the longitudinal axis of one of the saw head openings 130.A circular lip 134 formed integrally with saw head 68 defines the baseof opening 134. Lip 134 also defines an opening 135 from bore 133 intothe center of the saw head 68.

Saw head 68 also has a distal end section 136. The distal end section136 has a planar top surface 138. The most forward section of topsurface 138, section 140, has a rectangular profile. Extendingproximally rearward, top surface 138 has a section 142 with opposedoutwardly extending side edges such that width of the surface increasesextending proximally rearwardly from section 140. Rearward from section142, head top surface 138 has a section 144. The opposed side edges ofsection 144 taper inwardly such that the width of section 144 decreasesextending proximally rearward along the section.

Saw head 68 is provided with two pairs of L-shaped brackets 146 and 148that extend upwardly from and over top surface section 144. The bracketsforming each bracket pair 146 and 148 are opposed from and directedinwardly towards each other so that the end of each bracket extends overthe top surface 138. The brackets forming pair 146 are located in theforward part of top surface section 144 immediately proximal to wheretop surface 138 transitions from section 142 to section 144. Thebrackets forming bracket pair 148 are located immediately forward of theproximal edge of top surface section 144.

From FIG. 7A it can be appreciated that the brackets 146 and 148 areformed to have inner vertical surfaces 147 and 149, respectively, thatextend up from saw head top surface 138. The brackets 146 and 148 areoriented so that surfaces 147 and 149 are angled inwardly along linesthat are angled relative to the longitudinal axis of the saw head. Thuseach pair of surfaces 147 and pair of surfaces 149 are on lines thatintersect at points that are proximal extensions of the saw headlongitudinal axis. In the illustrated version of the invention, brackets146 and 148 are further oriented so that the surfaces 147 and 149 oneach side of the saw head are collinear.

Below top surface section 144 and the proximal half of portion 142, sawhead 68 has a curved surface 150 with a constant radius. Below thedistal half of top surface section 142 and top surface section 140, thesaw head 68 is shaped so that surface 150 merges into two opposedgenerally planar side cheeks 152. Immediately below top surface distalend portion 140, the saw head 68 is shaped to form a nose 154. Nose 154has a cross sectional profile that, extending downwardly from topsurface portion 140 approximates the shape of the top surface portion140. Below nose 154, saw head 68 is shaped so that a curved chin 156extends between side cheeks 152. The saw head 68 is further shaped sothat chin 156 is recessed relative to nose 154.

Saw head 68 is further shaped to define five longitudinally extendingcontiguous bores 160, 162, 164, 166 and 168. Bore 160 is the mostproximal of the saw head bores and forms a proximal end opening into thesaw head 68. The bore 160 is located in the saw head proximal endsection 124. Bore 160 is axially centered along the longitudinal centeraxis of the saw head 68. The saw head 68 is shaped to have an inner wallsection 161 that forms the proximal end opening into bore 160 that isprovided with threading (threading not illustrated). Not identified isthe groove between inner wall section 161 and the more distal portionsof the inner wall that defines bore 160. This groove is present formanufacturing purposes.

Bore 162 is contiguous with, coaxial with and extends distally forwardfrom bore 160. Bore 162 is located within the first and second saw headintermediate sections 128 and 132, respectively. The bore 162 has adiameter larger than that of bore 160. Both saw head openings 130 andthe opening 135 open into bore 162. The bore 164 is contiguous andcoaxial with and projects distally forward from the bore 162. The sawhead 68 is shaped so that bore 164 has a diameter equal to the diameterof bore 160. Bore 164 is formed in the portion of the saw head subtendedby curved surface 150.

Bores 166 and 168 are partially overlapping closed end bores that bothextend longitudinally distally forward from the front of bore 164. Bore166 is the longer of the two bores 166 and 168. Bore 166 extends intothe saw head nose 154. Thus, bore 166 is not coaxial with bores 160, 162and 164. The bore 168 is located below and partially overlaps bore 166.Bore 168 only extends a relatively short distance forward of bore 164.Bore 168 terminates at the surface of a web 170 internal to the saw head68.

The saw head 68 is further formed to have two contiguous openings 172and 174 in the top surface portion 144. Opening 172 forms a recess inthe top surface. The opening 172 is approximately rectangularly shapedsuch that the longitudinal axis of is parallel with the longitudinalaxis of the saw head 68. While opening 172 is generally rectangularlyshaped, the longitudinally extending sides do have outwardly extendingapices (not identified) that are centered on the longitudinal axis ofthe opening. The apex of the proximally directed edge is directedproximally; the apex of the distally directed edge is directed distally.Opening 174 extends downwardly from the base of opening 172 into sawhead bore 164. Opening 174 is oval shaped and subtends less area thanopening 172.

A bore 176 extends upwardly from the bottom of the saw head 68 at alocation proximal to distal facing chin 156. Bore 176 opens into thelongitudinally extending bore 166. A bore 178 extends downwardly fromthe saw head top surface portion 140 into bore 166. The bore 178 iscoaxial with and has a smaller diameter than bore 176. It will furtherbe noted that saw head 68 is formed to have a small annular inwardlydirected lip 179 projects into bore 176. Lip 179 forms the base of bore178

When saw 50 is assembled, the saw head 68 is fit into the motor housing80 so that the proximal end section 124 fits in the motor housing thirdbore 92 as best seen in FIG. 3. Two sets of ball bearings 182 facilitatethe rotation of the saw head 68 relative to the motor housing 80. Afirst set of bearings 182 extend around the saw head proximal endsection 124 in a circle that is immediately distal to the proximal endof the saw head. These bearings 182 are sandwiched between an inner race184 and an outer race 186. The inner race 184, seen in FIG. 9, has aring shaped main body 188. A flange 190 extends radially outwardly fromthe main body 188. The flange 190 is located closer to the distal end ofthe race main body 188 than the proximal end. The inner race 188 isfurther formed to have a distally facing, outwardly tapered surface 192that extends from flange 190 to the distal end of the main body 188.

FIG. 10 illustrates outer race 186. Generally, outer race 186 is in theform of a ring. The outer race 186 is further formed to define acircumferential groove 187 that is located proximal of the distallydirected front end of the race and that extends around the innerperimeter of the race.

When the saw 50 of this invention is assembled, the outer race 186 isseated against the circular stepped inner surface of the motor housing80 that defines the transition between the second and third bores 90 and92, respectively. Ball bearings 182 are fitted in annular groove 187.Inner race 184 is fitted over the saw head proximal end section 124 sothat tapered surface 192 presses against the ball bearings 182.

A wave spring 181, seen in FIG. 3, extends between the proximallydirected face of inner race flange 190 and a head retainer ring 193. Asseen in FIG. 11, head retainer ring 193 has a sleeve like main body 194the outer surface of which is threaded (threading not illustrated). Anannular lip 195 extends radially outwardly from the distal end of ringmain body 194. Ring lip 195 is formed with notches (not identified) tofacilitate use of a fastening tool. During assembly of the saw 50, thehead retainer ring main body 194 is screw secured to the complementarythreading around proximal end section 161 of saw head bore 160. Theproximal end of the wave spring 181 seats against the static, forwardfacing surface of ring lip 195.

Wave spring 181 thus imposes a forward directed force on the inner racethat presses the flange tapered surface 192 against the ball bearings182. The lip 195 of the head retainer ring 193 functions as thestructural member that holds the saw head 68 to the motor housing 80.

The forwardly-located set of ball bearings 182 seat against the annulartapered surface 126 of the saw head. An outer race 196 disposed in themotor housing distal most, fourth bore 94 of the motor housing 80 alsosurrounds this set of ball bearings 182. The outer race 196, best seenin FIGS. 12 and 13 has a circular, proximally located base ring 198. Theouter race base ring 198 is shaped to tightly press fit in the motorhousing fourth bore 94. Base ring 198 is further shaped to have acircumferentially extending lip 202. When the saw 50 is assembled, theouter race 196 is positioned in motor housing bore 94 so that the outersurface of lip 202 seats against the inner surface of the motor housingthat defines bore 94. Collectively, lip 202 and the adjacent innersurface of the race base ring 198 are shaped to define a groove 204 thathas an inwardly shaped profile. The outer race 196 is shaped so thatgroove 204 has a radius that accommodates the seating of ball bearings182.

Outer race 196 is further formed to have a cylindrical skirt 206 thatextends distally forward of the base ring 198. The skirt 206, which isintegral with the base ring 198, has an outer diameter less than that ofthe base ring. Outer race skirt 206 is further formed so that the mostforward section thereof has inner wall that is outwardly steppedrelative to the remaining proximally located section. In the Figures,annular, radially extending step 208 defines the transition between thetwo wall sections. Step 208 thus divides the race skirt 206 into a thickwalled section and a smaller thin walled section. The outer race isfurther formed to define a number of circumferentially equangularlyspaced apart openings 210. Each opening 210 has a rectangular crosssection and extends longitudinally through a thick walled portion of theskirt 206 and a small portion of the adjacent outwardly stepped thinwalled section.

When the saw 30 is assembled, the distal most ball bearings 182, inaddition to seating against saw head tapered surface 126, seat in outerrace groove 204.

During assembly, motor housing 80 is fitted to the saw front plate 64.Specifically, the motor housing is fitted to the front plate 64 so thatthe housing first collar 84 seats in an opening 212 formed in the frontplate 64. A threaded ring 214, best seen in FIGS. 4 and 14, is fittedover the housing second collar 86 to hold the motor housing to the frontplate 64. Ring 214 is formed with a circular skirt 216 that forms themain body of the ring. The inner cylindrically shaped wall of ring skirt216 is formed with threading, not illustrated. The ring 214 is furtherformed so that skirt 216 has an outwardly flared outer wall. A circularlip 218 extends inwardly from the distal end face of skirt 216.

While not illustrated, it should be understood that an anti-rotation pinmay be fitted in a groove formed in the outer surface of the motorhousing 80. This pin extends beyond the perimeter of the cylindricalmotor housing 80 into a complementary notch formed in the front plate64. This notch is contiguous with and extends beyond the perimeter ofplate opening 212. The pin thus prevents rotation of the motor housing80 relative to the front plate 64.

At assembly, the ring 214 is screw fitted over the motor housing secondcollar 86. The proximally facing base of ring skirt 216 bears againstthe adjacent distally directed face of the front plate 64. This actioncauses the motor housing 80 to move forward until the laterallyextending stepped surface of the housing 80 between main section 82 andthe first collar 84 bears against the inner, proximally directed face ofthe front plate 64. The motor housing 80 is thus compression locked tothe front plate 64 by the annular step around the motor housing firstcollar 84 and ring 214.

During the process of assembling saw 50, blade drive assembly and bladecoupling assembly components described below are assembled into the sawhead 68. Saw head proximal end section 124 is then fitted to the motorhousing 80 to extend through the housing third bore 92 so as to projecta short distance into the second bore 90. Retaining ring 193 is screwfitted to the complementary threading around the saw head inner wallsection 161. Prior to the coupling of the retaining ring 193 inposition, the proximal located ball bearings 182, the inner race 184 andwave spring 181 are positioned around the saw head proximal end section124.

An indexing lock link 224, now described by reference to FIGS. 15 and16, holds the saw head 68, and the components disposed therein, at afixed angular orientation relative to the longitudinal axis of the motorhousing 80. Lock link 224 includes a base 226 in the form of arectangular bar. At the proximal end, a lock tongue 228 extends upwardlyfrom base 226. Lock link tongue 228 is in the form of rectangular blockdimensioned to closely slip fit into one of the rectangular openings 210of outer race 196. The lock link 224 is further shaped to have a post230 that extends upwardly from the base 226 at a location proximal tothe distal end of the base.

As seen in FIG. 17, the lock link 224 is seated in saw head bore 162.Lock link 224 is positioned so that post 230 extends through opening 135into bore 133. Lock link tongue 228 extends through the adjacent opening130 formed in the saw head 68. A release button 232 is secured over theexposed end of post 230. A coil spring 234 extends between the undersideof the release button 232 and the adjacent static annular lip 134 of thesaw head 68 that defines the base of bore 133. Spring 234, by workingagainst button 232, exerts an outward force on the lock link 224. Thisforce normally causes base 226 to seat against the inner surface of thesaw head that defines bore 162 so that tongue 228 normally projectsthrough opening 130.

When the saw 50 is assembled, the saw head openings 130 are aligned withthe cross sectional slice section of the motor housing 80 in which theopenings 210 of outer race 196 are located. Lock link tongue 228, whenit extends through the saw head opening 130, seats in one of the raceopenings 210. This engagement of the lock link 224 with the outer race196 locks the saw head 68 in a fixed angular orientation relative to thelongitudinal axis of the motor housing. The depression of button 234causes lock link 224 to move towards the center of saw head 68. Thiscauses the link tongue 228 to retract out of the race opening 210 inwhich it is seated so as to release the saw head from the lockedposition. The surgical personnel can then rotate, index, the saw head 68to the desired angular orientation. Once the saw head 68 is sopositioned, button 232 is released. Spring 234 moves the lock link backto the locked state so the tongue 228 seats in the adjacent race opening210 to again hold the saw head in position.

III. Blade Drive Assembly

An output shaft 240 disposed in the saw head 68 receives the rotationmoment output by the motor rotor 98. A bearing assembly, also internalto saw head 68, converts the rotary moment into motion that oscillatesoscillating shaft 242 also located in the saw head. Oscillating head 70is coupled to the oscillating shaft 242 to move in unison with theoscillating shaft.

In more detail, the output shaft 240, seen best in FIGS. 18 and 19, is asingle elongated solid piece of metal. At the most proximal end, outputshaft 240 is shaped to have a generally rectangularly shaped stem 244.Forward of stem 244, output shaft 240 has a cylindrical main section246. The center axis of the main section is aligned with the centerlongitudinal axis of stem 244. The main section 246 is formed to have aproximal end portion 248 that is provided with threading (notillustrated). Not identified is the annular groove between the shaftproximal end portion and the remaining more distally located portion.The groove facilitates manufacture of the output shaft 240.

Forward of and coaxial with the main section 246, the output shaft 240is formed to have a collar 252 Collar 252 has an outer diameter greaterthan that of main section 246. A neck 254 with a diameter less than thatof shaft main section 246 extends forward from the collar 252.

A shaft head 256 projects forward of the collar 252. The output shaft240 is formed so that head 256 is not coaxial with the more proximallylocated sections of the shaft. Instead, shaft head 256, which iscylindrical in shape, is centered on an axis that is betweenapproximately 5 and 7° off set from the longitudinal axis through theshaft main section. Further, shaft head 256 extends forward from neck254 at a such that, as seen in FIG. 19, the longitudinal axis of thehead, represented by line 258, does not extend from the distal endterminus of the longitudinal axis that extends through the shaft mainsection 246, collar 252 and neck 254, (line 258). Instead, shaft head256 is positioned so that the head longitudinal axis intersects a line,dashed line 262, representative of the extension of the primarylongitudinal axis at a point forward of the shaft neck section 254.

A nose 264 extends forward from the free distal end of the shaft head256. Threading, not illustrated is formed over the outer cylindricalsurface of nose 264.

Output shaft 240 is rotatably mounted in a rear inner housing 268 thatis slidably fitted in the saw head bore 160. As seen in FIG. 20, therear inner housing 268 is a multi-section structure. The most proximalsection of the rear inner housing is a base 270. The base 270 has anouter diameter that facilitates the close sliding movement of the basein the saw head proximally-located bore 160. One or more notches 271(one seen) extend distally inward from the proximal end of the base 270.Notches 271 facilitate the use of an assembly/disassembly tool (notillustrated).

Extending forward from base 270, rear inner housing 268 has a generallycylindrical stem 272. The stem 272 has an outer diameter that is lessthan that of the base 270. While not illustrated, the rear inner housingstem 272 may be formed with windows to reduce the overall weight of therear inner housing 268. The rear inner housing 268 is formed to have ahead 274 located immediately distally forward of the stem 272. Head 274has an outer diameter between that of the base 270 and the stem 272. Theouter surface of the rear inner housing head 274 is provided withthreading (not illustrated). A nose 276 forms the most distal section ofthe rear inner housing 268. Nose 276, which is located immediatelyforward of head 274, has a diameter between that of the stem 272 and thehead 274.

Rear inner housing 268 is further formed to have proximal and distalbores 278 and 280, respectively. Proximal bore 278 is located within thehousing base 270. The distal bore 280 extends through the housing stem272, head 274 and nose 276. Distal bore 280 has a diameter less thanthat of the proximal bore 278. The rear inner housing is further formedso that, within the base 268 at the distal end of the base, there is anannular, inwardly extending ledge 282. Ledge 282 separates the distalend base of proximal bore 278 between the proximal end base of thedistal bore 280. The inner edge of ledge 282 defines an opening 284 inthe rear inner housing 268 between the proximal and distal bores 278 and280, respectively. Opening 284 has a diameter less than that of thedistal bore 280.

Two bearing assemblies 286 and 288, seen best in FIG. 4, rotatably holdoutput shaft 240 in the rear inner housing 268. Bearing assembly 286,the proximal of the two assemblies, is disposed over the smoothed walledportion of the shaft main section 246 immediately forward of proximalend portion 248. Bearing assembly 288, the distal-located bearingassembly, is positioned over the shaft main section 246 immediatelyproximal to the shaft collar 252. A sleeve-shaped spacer 290 extendsbetween the outer races of the bearing assemblies 286 and 288 to holdthe assemblies apart. (The individual races of bearing assemblies 286and 288 not illustrated.)

A retaining nut 292 holds the bearing assemblies 286 and 288 and spacer290 to the output shaft 240. Nut 292 threads over the threading formedon the shaft main section partial end portion 248 to abut the inner raceof bearing assembly 286. When saw 50 is assembled, the outer race ofbearing assembly 286 seats against the distally directed face of rearinner housing ledge 282. The shaft stem 244 extends through the rearinner housing bore proximal bore 278 and a short distance into thecenter void of the head retainer ring main body 194.

A drive coupler 296 attached to the motor rotor 98 couples the outputshaft 240 to the rotor so the two components rotate in unison and theshaft 240 can longitudinally move relative to the rotor 98. As seen inFIG. 21, drive coupler 296 is formed from a single piece of metal and isformed to have a tubular stem 298. Stem 298 is dimensioned to be pressfit in rotor bore 109 so that the rotor 98 and drive coupler 296function as a single unit. The stem 298 is formed with a bore 299. Bore299 is present to relieve the stress associated with the press fittingof the stem 298 in motor rotor bore 109. Forward of stem 298, the drivecoupler 296 has a collar 302. Collar 302 has a diameter greater thanthat of rotor bore 109 to limit the extent to which the drive coupler296 is press fit into the rotor bore.

Forward of collar 302, drive coupler 296 has a cylindrical head 304.While the drive coupler head 304 is generally solid, the head is formeddefine a slot 306 that extends diametrically across the head. Slot 306has a width that allows the output shaft stem 244 to slidably movewithin the slot. Upon assembly of the saw 50, the output shaft stem 244is slidably fitted in drive coupler slot 306 so that, upon rotation ofthe motor rotor 98, the output shaft 240 rotates with the rotor.

A front inner housing 310 surrounds the distal end of the rear innerhousing 268 and the portions of the output shaft 240 forward of the rearinner housing. Front inner housing 310 is the component to which theoscillating head 70 and oscillating shaft 242 are rotatably mounted. Asbest seen in FIGS. 22-24, front inner housing 310 includes a base 312.Generally, base 312 has a cylindrical shape. The outer diameter of thefront inner housing base 312 is dimensioned to allow the base toslidably fit in saw head bore 164. Base 312 is further shaped so that,forward the proximal end, the base defines two windows 314 into thecenter of the base. Base 312 is further formed to have two opposednotches 316 that extend inwardly from distally directed front face ofthe base. Both windows 314 and notches 316 are provided to facilitatemanufacture of the saw 50.

Front inner housing base 312 is further formed to have a number of boresand openings. A first bore 318 extends forwardly inward from theproximal end of the base 312. The circular inner wall of base 312 thatdefines bore 318 is provided with threading, (not identified). Morespecifically, the inner housing base 312 is formed so that the threadingaround bore 318 can screw secure this bore-defining section of the innerhousing 268 to the adjacent rear inner housing head 274. Immediately infront of bore 318, front inner housing 310 has a second bore 320. Bore320 has a diameter greater than that of bore 318. Bore 320 exists as aresult of the manufacturing processes and is not otherwise material tothis invention.

Forward of bore, 320, the front inner housing base 312 is shaped to havea bore 322. Bore 322 has a diameter less than that of the proximal endbore 318. More specifically, the front inner housing 310 is formed sothat base 312 is shaped so that the rear inner housing nose 276 cansnugly fit in bore 322. A closed end bore 324 extends distally forwardof bore 322. Bore 324 has a diameter less than that of bore 322. Itshould be appreciated that bores 320, 322 and 324 are coaxial with thelongitudinal axis of the rear inner housing base 312. Windows 314 openinto bores 322 and 324.

The front inner housing base 312 is formed with opposed, axially alignedtop and bottom openings 330 and 332, respectively, which extend intobore 324. During manufacture of front inner housing 310, material isleft to define around the bases of opening 330 and 332 arcuately shaped,diametrically opposed ledges 334 and 336, respectively. Ledges 334extend into the space immediately below the base of opening 330. Ledges336 extend into the space immediately above the base of opening 332.

Front inner housing 310 is further formed to have a bore 338 thatextends inwardly, proximally rearward from the distally directed frontface of base 312. Bore 338 is closed ended and terminates on theopposite side of the interior wall of the housing base at which bore 324terminates.

Formed integrally with and extending forward from base 312, front innerhousing has a nose 342. In FIG. 23, the nose 342 is shown extendingforward from a generally circular boss 344 that itself extends forwardfrom the front face of the base 312. Bore 338 intersects boss 344. Boss344 exists as a result of the processes employed to machine the frontinner housing 310 and is not otherwise relevant to this invention.

Nose 342 is in the form of an elongated plate. Nose 342 is furtherformed to have opposed longitudinally extending side edges 346 that aresymmetrical inwardly curved. The radius of curvature of the race noseside edges 346 matches the radius of surrounding saw head bore 166 andthe nose is free to move in bore 166. The front inner housing nose isalso formed to have a longitudinally extending oval through slot 348.Opening 348 is centered on the longitudinal axis of the nose 342.

As best seen in FIGS. 25-27 and 27A, oscillating shaft 242 includes aring shaped center section 352. The outer surface of shaft centersection 352 is generally in form of slice section through the center ofa sphere; the outer surface is curved along two perpendicular radii.Center section 352 is further formed to have two opposed surfaces 354 onthe outside of the section 352 along the middle of the section. Surfaces354 have outer surfaces that are curved along a single radius thatextends perpendicularly from the longitudinal axis of the shaft. Shaftcenter section 352 is further formed to define an opening 356 thatextends through one of the surfaces 354. Shaft center section 352 isalso shaped so to define a chamfer 358 on the side opposite the side inwhich opening 356 is formed. Chamfer 358 extends outwardly from theinner wall of the cylindrical inner wall that defines the openingthrough the center section 352.

Center section 352 is further formed to have a recessed surface 359 thatextend inwardly from the generally cylindrical inner wall of the centersection. The recessed surface 359 is formed by a ball mill cut process.Recessed surface 359 is formed to facilitate assembly of the componentsforming the blade drive assembly.

Oscillating shaft 242 is further formed to have diametrically opposed,axially aligned, cylindrically shaped head 360 and stem 362 that extendoutwardly from the center section 352. Head 360 is formed with adownwardly extending closed end threaded bore 364. Stem 362 is formedwith a threaded through bore 366 (threading not shown) that extends intothe enclosed circular space defined by the center section. Theoscillating shaft 242 is further formed to define notches 368 thatextend inwardly from one of the outer faces of the center section tohead 360. The shaft is formed so that the surfaces that define the sidewalls of notches 368 taper inwardly toward each other.

As seen in FIGS. 28 and 29, the oscillating head 70 is formed to have anelongated top plate 370. Top plate 370 is shaped to be widest along thelateral axis of the plate and narrowest at the opposed ends. The ends oftop plate 70 are curved. Pins 72 extend upwardly from the opposed sidesof the top plate 70. Oscillating head 70 is further formed to have acircular boss 374 that extends downwardly from the center of the topplate 370. Boss 374 has a first section 376 immediately adjacent the topplate 70 with a first diameter. Below the first section 376 there is aboss second section 378. The boss second section 378 has a diameter lessthan that of the first section 376. Boss 374 is further formed to have athird section 380 immediately below the second section. Below the bossthird section 380, oscillating head 70 is formed to have a pair ofdiametrically opposed, spaced apart feet 382 (one shown in FIG. 29).

Oscillating head 70 is further formed to have a bore 384 that extendsupwardly between feet 382 and through boss 374. The oscillating headbore 384 is shaped to facilitate therein in close sliding fit, if notcompression fit, the oscillating shaft head 360. More particularly, theoscillating head 70 is formed to define first and second counterbores386 and 390, respectively, located above bore 384. First counterbore 386is formed in the portion of the boss first section 376 immediately belowthe head top plate 370. First counterbore 386 has a diameter greaterthan that of bore 384. Second counterbore 388 forms the opening intobore 384 through the top plate 370. The second counterbore 388 has adiameter between that of bore 384 and first counterbore 386. Secondcounterbore 388 is provided with threading to facilitate attachment of adisassembly tool (threading and tool not illustrated).

The oscillating head 70 and oscillating shaft 242 are coupled togetherby fitting the shaft head 360 in the oscillating head bore 384. Theoscillating head feet 382 are seated separate oscillating shaft notches368. The seating of the feet 382 in notches 368 blocks the rotation ofthe oscillating head 70 relative to the shaft 242. A shaft screw 391 isscrew secured in the oscillating shaft head bore 364. As seen in FIG.30, shaft screw 391 has a cylindrical shaft 392. The outer surface ofscrew shaft 391 is provided with threading, (not illustrated) to screwsecure the shaft into the oscillating shaft head bore 364. Above foot392, shaft screw 391 is formed with a head 394 that is the widestdiameter portion of the screw. More particularly, the shaft screw 391 isformed so that the downwardly directed annular outer face of the head394 disposed around the shaft 392 the adjacent annular stepped surfaceof that defines the base of the oscillating head first counterbore 386.

Notches 396 (two shown in FIG. 30) are formed in screw head 394 toextend longitundally along the outer perimeter of the head. Notches 396are provided to receive a fastening tool.

Returning to FIG. 4, it can be seen that the oscillating shaft andoscillating head sub-assembly extends through front inner housing topopening 330, bore 324 and bottom opening 332. A bearing assembly 398rotatably holds the oscillating head 70 in the front inner housingopening 330. More particularly, the outer race of bearing assembly 398(races not explicitly identified) fits against the inner circular wallof the front inner housing 310 that defines opening 330. The inner raceof the bearing assembly 398 surrounds the third section 380 of boss 374integral with oscillating head 70. Downward movement of the bearingassembly 398 is limited by the abutment of the assembly outer raceagainst the opposed ledges 334. The annular, downwardly directed face ofthe second section 378 of the oscillating head boss 374 presses againstthe top surface of the inner race of bearing assembly 398. Thus, frontinner housing ledges 334 and oscillating head boss 374 collectivelycooperate to prevent longitudinal movement of bearing assembly 398.

A bearing assembly 402 rotatably couples the oscillating shaft 242 infront inner housing opening 332. The outer race of bearing assembly 402is disposed around the perimeter wall of opening 330. The inner race ofbearing assembly 402 (races not explicitly identified) seats overoscillating shaft stem 362. The upwardly directed face of the outer raceabuts against the opposed front inner housing ledges 336. A screw 404 isthreaded into bore 366 integral with the oscillating shaft stem 362. Thehead of screw 404 bears against the downwardly directed face of theinner race of bearing assembly 402. Thus front inner housing ledges 336and screw 404 collectively cooperate to prevent longitudinal movement ofthe bearing assembly 402.

Collectively, bearing assemblies 398 and 402 hold the oscillating headand shaft 70 and 242, respectively, to the saw head 68 so that thesecomponents can rotate about their colinear longitudinal axes.

A wobble ring 406 is part of the assembly that transfers the rotationalmoment of the output shaft 240 into motion that oscillates theoscillating shaft 242. The wobble ring 406 is disposed over the outputshaft head 256 and seated in the oscillating shaft center section 352.Wobble ring 406, seen in FIGS. 31-33, output includes a ring shaped base408. The inner circular surface of the ring base 408 has a linearprofile. The outer circular surface of the ring base 408 has a profileof a slice section through the center of a sphere. Wobble ring base 408is further formed to have on the sides, two diametrically opposedsurfaces 410. Surfaces 410 have single curvature, around a radiusperpendicular to the longitudinal axis of the wobble ring. Wobble ringbase 408 is further formed to have a flat 411 located between opposedsurfaces 410. Surfaces 410 and flat 411 exist for manufacturing reasons.

The wobble ring 406 is further formed to have a head 414 that isdisposed above the base 408. The head 414 is connected to the base by apost 412. In the illustrated version of the invention, post 412 has agenerally conical shape. The post 412 extends upwardly from the base ata position diametrically opposite flat 411. Head 414 is shaped to havegeometry that equal to that of a truncated sphere. Opposite post 412,wobble ring base 408 is formed to have an opening 416 through flat 41.Opening 416 is provided for assembly purposes.

A bearing assembly 418, seen in FIG. 4, is disposed over the outputshaft head 256 rotatably couples wobble ring 406 to the shaft head. Afastener 420 disposed over the output shaft nose 264 holds the wobblering 406 and bearing assembly 418 to the output shaft 240.

Upon assembly, the wobble ring 406 is seated in the oscillating shaftcenter section 352 so that wobble ring head 414 seats in shaft opening356. As a result of this engagement, when the output shaft 240 rotates,the wobble ring is prevented from rotating with the output shaft 240.Instead, the wobble ring 406 oscillates back and around the point wherethe line that extends from intersection of axis of the main body of theoutput shaft 240 and the axis of the shaft head 256. This oscillatorymovement is transferred through the wobble ring 414 to oscillating shaft240.

A coil spring 422, (seen only in FIG. 2) is disposed in the saw head 68.One end of the spring 422 seats against the interior wall of the sawhead 68 that defines the base of saw head bore 168. (While not shown, itshould be appreciated that the distal end of spring 422 may seat againsta back plate disposed against the base of saw head bore 168.) Theopposed end of spring 422 seats in the bore 338 that extends inwardlyfrom the distally directed face of the front inner housing 310. Spring422 urges the front inner housing 310 and the components attachedthereto rearwardly away from the saw head nose 342. The components urgedproximally rearwardly with the front inner housing include theoscillating head 70, output shaft 240, oscillating shaft 242 and rearinner housing 268. Spring 422 is selected so that the force imposed bythe spring can be overcome by manual force. Further designconsiderations that contribute to the selection of spring 422 arediscussed below.

III. Blade Coupling Assembly

A coupling rod 428 slidably mounted to the saw head 68 releaseably holdsthe blade assembly 52 to the saw. As seen in FIGS. 34 and 35, couplingrod 428 is formed to have a cylindrical, bottom located stem 430. Theouter circumferential surface of stem 430 is formed with threading (notillustrated). Above stem 430, rod 428 has a leg 432 with a diameter lessthan that of the stem. Located immediately above leg 432, rod 428 has amain body 434. The main body 434 generally has a circular crosssectional shape with a diameter greater than that of the stem 430.Coupling rod 428 is further formed so that the rod main body 434 has twodiametrically opposed longitudinally extending flats 436 (one shown).Each flat 436 extends upwardly from the lower base of the rod main body434 to have overall length approximately 65 to 85% the length of themain body.

Above main body 434, coupling rod 428 has a circular collar 438. Thecollar 438 has an outer diameter greater than that of the main body 434.A neck 440 projects above collar 438. Neck 440 has a diameter less thanthat of the collar 438. A circular head 442 forms the top most sectionof the coupling rod 428. The head 440 has a diameter greater than thatof neck 440 and slightly less than that of the rod collar 438. In theillustrated version of the invention, the outer perimeter surface of thehead 442 located above the neck 440 extends outwardly, the outerperimeter surface of the head that extends downwardly from the top ofthe head similarly tapers outwardly, (tapered surfaces not identified.)

Coupling rod 428 extends through saw head bores 178 and 166 and into sawhead bore 176. The coupling rod 428 also extends through slot 348 formedin the front inner housing nose 342. More specifically, the coupling rod428 is dimensioned so that the distance between the main body flats 436is slightly less than the width across slot 348. This allows thecoupling rod 428 to move within the slot 348; the limited slot widthblocks rotation of the coupling rod.

A spring 446 (seen only in FIG. 4) is disposed around the upper end ofthe coupling rod main body disposed in saw head bore 178. One end ofspring 444 seats in the lip 179 that forms the base of bore 178. Theopposed end of the spring 444 presses against the downwardly directedannular surface of the coupling rod collar 438 that surrounds the mainbody 434.

A wing nut 448 and a wing nut retainer 450 surround the end of thecoupling rod 428 disposed in saw head bore 176. As seen best in FIGS. 36and 37, wing nut 448 includes an elongated bar 452. Not identified arethe concave opposed surfaces on the bar 452 that function asfinger/thumb grasping surfaces. A circular boss 454 extends upwardlyfrom one of the side edges of the bar into saw head bore 176. Boss 454is dimensioned to rotate in saw head bore 176. The wing nut 448 isfurther formed to have a bore 456 that extends through boss 454 andpartially into the underlying section of wing nut bar 452. Bore 456opens into a coaxially extending bore 458 that extend through to theopposite edge of bar 452. Bore 458 has a larger diameter than bore 456.

Wing nut 448 is further formed so that two diametrically opposed tabs460 extend upwardly from the exposed annular face of boss 454. Tabs 460are shaped to have heads with a semi-circular cross sectional shape (tabheads not identified).

The wing nut retainer 450, seen best in cross section in FIG. 38, has ahead 462 from which an elongated shaft 464 extends. Head 462 is formedwith a diametrically extending slot 466 for receiving the blade of screwdriver. The outer surface of shaft 464 is smooth walled and dimensionedto slidably fit in wing nut bore 456. A bore 468 extends inwardly fromthe free end of the shaft towards head 462. The inner wall of the wingnut retainer that defines bore 468 is provided with threading (notillustrated).

When saw 50 is assembled the coupling rod stem 430 is screw secured inwing nut bore 468 as seen in FIG. 44. As part of the assembly process, aset of Bellville washers 470 are seated in wing nut bore 458 around wingnut retainer shaft 464. The Bellville washers 470 extend between theinternal annular surface of the wing nut 448 that defines the base ofbore 458 and head 462 of the wing nut retainer 450. In the illustratedversion of the invention, ball bearings 471 are disposed between thebottommost Bellville washer 470 and the wing nut retainer head 462. Inactuality, the ball bearings 471 are sandwiched between the wing nutretainer head 462 and a ring-shaped race 472 disposed around thebottommost Bellville washer 470. Ball bearings 471 facilitate therotation of the wing nut 448 and Bellville washers 470 around the wingnut retainer 450.

In some versions of the invention, the ball bearings 471 are disposedbetween the topmost Bellville washer 470 and the adjacent annularsurface of the wing nut 458 that defines bore 468.

A cam 474 is slidably disposed over the coupling rod main body 434between the front inner housing nose 342 and the wing nut boss 454. Asseen in FIGS. 39, 40 and 41, cam 474 has a sleeve shaped main body 476.A head 478, also sleeve shaped, projects above main body 476. Cam head478 has an outer diameter less than that of the main body 476. Twodiametrically opposed, spaced apart teeth 479 extend upwardly from theannular exposed face of the head. The outer surfaces of teeth 479 areflush with and have the same radius of curvature of the head 478.Collectively, cam main body 476 and head 478 define a common constantdiameter through bore 477.

Cam 474 is further shaped to define at the base of the main bodydiametrically opposed cam surfaces. Each cam surface is shaped to have aconcave notch 480. The notch 480-defining surfaces define a radiusmarginally greater that the radius of curvature of wing nut tabs 460. Onone side of each notch 480, the cam surface defines a vertical wall 482.On the opposed side of the notch 480, the cam surface is shaped todefine a small indentation 484 followed by a downwardly directed slopingwall 486. From the sloping wall 486, each cam surface defines a detent488. Beyond detent 488, each cam surface defines a notch 490. For eachcam surface, notch 490 is, relative to the notch 480, spaced furtheraway from the cam head 478. The portion of the cam surface that definesnotch 490 is the end portion of the cam surface. Notches 490, likenotches 480, are dimensioned to receive the wing nut tabs 460. Theportion of cam main body 476 that forms the vertical wall 482 of a firstcam surface defines a similar vertical wall 491 of the second camsurface.

Upon assembly of the saw 50, cam 474 is fit over the coupling rod mainbody 434. The cam 474 is positioned so that the cam teeth 479 aredisposed in nose slot 348 of the front inner housing 310. The seating ofthe cam teeth in slot 348 blocks rotation of the cam 474. Each wing nuttab 460 seats against a separate one of the cam surfaces. When thecoupling assembly is positioned to hold the blade assembly, the run orlocked position, each wing nut tab 460 is seated in the notch 490 of theassociated cam surface. When the coupling assembly is in the load orunlocked state, in which the blade can be removed and replaced, the wingnut 448 is rotated so nut tabs 460 are positioned in the complementarynotches 480.

As seen in FIG. 42, when the coupling assembly is in the load state, cam474 is positioned so that the arcuate top faces of the face of the camhead 478 are spaced away from the undersurface of the front innerhousing nose 342. Owing to the force placed on the coupling rod 428 byspring 446, the rod is positioned so that the rod head 442 above the sawhead top surface 138.

IV. Blade Assembly

The construction of the blade assembly 52 of this invention is nowexplained by reference to FIGS. 1 and 43. Specifically, the bladeassembly 52 includes an elongated, flat static bar 494. The proximal endof bar 494 is the component of the blade assembly 52 mounted to the sawhead top surface 138. Blade head 76 has a proximal end base 496 that isdisposed in the distal end of bar 494. A crown 498, integral with andextending forward from the base 496, is the most distal portion of theblade head 76. The crown 498 projects forward beyond the distal end ofthe bar 494. The outer distal edge of the crown is formed with the bladeteeth 150 (shown schematically) that perform the actual cutting action.

Blade bar 494 is formed from lower and upper plates 502 and 504,respectively. The lower plate 502 has a proximally located base 506,generally in the form of trapezoid, wherein the opposed lateral sideedges are symmetric and taper inwardly towards the proximal end edge ofthe plate 502. The lower bar base 506 is further formed to defineopposed notches 508 that extend inwardly from the side edges of thebase. Within the section of the base 506 between notches 508, lowerplate base 506 is further formed to have an oval shaped opening 510 andtwo oval shaped openings 512. Opening 510 is centered along thelongitudinal axis of the lower plate 502. The openings 512 are locatedon the opposed sides of and are adjacent to opening 510. Thelongitudinal axes of openings 512 are parallel with the longitudinalaxis of opening 510. Openings 512 are longer than opening 510.

Forward of the base 506, the lower plate 502 is formed to have anintermediate section 513. The side edges of the intermediate sectiontaper inwardly as they extend forward. Plate intermediate section 513transitions into a constant width blade proximal section 514. The lowerplate 502 is further formed so as to define a keyhole-shaped opening 516that extends from the intermediate section 512 to the distal section514. Opening 516 is dimensioned so that the coupling rod head 440 canextend into the wide diameter distal portion of the opening. The opening516 is further shaped so that the narrow portion thereof has a widthless than the coupling rod head 442 and greater than that of rod neck440

The forward portion of the bar lower plate distal section 514 is formedwith a circular, upwardly extending boss 518. On either side of boss518, lower plate 502 defines an oval-shaped opening 520. Each opening520 is longitudinally aligned with a separate one of the openings 512.Lower plate 502 is also formed to have three pairs of L-shaped tabs 521.Each tab 521 is located immediately inward of the adjacent longitudinalside of the plate 502. Each tab 521 extends upwardly towards the upperplate 504. The tabs 521 are arranged in pairs such that one tab of eachpair is diametrically opposed to the second tab of the pair. A firstpair of tabs 521 is located along a line that is slightly proximal tothe mid line between opening 516 and openings 520. A second pair of tabs521 is located slightly proximal to openings 520. The third set of tabs521 is located distal from openings 521.

Forward of openings 520, the lower plate 502 is formed with twoadditional openings, discharge ports 522. More particularly, thedischarge ports 522 open from a section of the surface of the lowerplate that is subtended by the blade head base 496. Each discharge port522 is approximately in the shape of an oval. Lower plate 502 is furtherformed so that the discharge ports are centered on a common non-linearlongitudinal axis. More particularly this axis is curved. The radius ofcurvature of this axis is center in which the section of the blade head46 disposed underneath the ports oscillates. Discharge ports 522 aresymmetrically located around the longitudinal axis of the lower plate502.

The upper plate 504 is shaped to have the same general perimeter profileof the lower plate 502; the description of this profile is not repeated.Upper plate 504 is further formed to have a lip 526 that extendsdownwardly from the edges of the plate. Collectively, the plates 502 and504 are dimensioned so that when the upper plate 504 is disposed overthe lower plate 502, the upper plate lip 526 extends around the adjacentedges of the lower plate 502. The upper plate 504 is formed so that lip526 extends around the proximal end of the lower 502 plate and theopposed longitudinally extending side edges of the lower plate 502.Thus, upon assembly, blade bar 494 has a distal end opening between thelower plate 502 and the upper plate 504 (opening not identified).

Upper plate 504 is further formed to have two oval-shaped openings 528.Each opening 528 is identical in shape with and positioned to be aligneddirectly over one of the lower plate openings 512. An oval shapedopening 530 is also formed in upper plate 504. Opening 530 is identicalin shape with and positioned to be aligned directly over lower plateopening 510. Located proximally rearward of openings 528 and 530, theupper plate 504 is further formed to have a downwardly extending gusset532. Gusset 532 extends laterally across lower plate 504 at a locationimmediately forward of the proximal end of the plate.

Forward of openings 528 and 530, the upper plate 504 is formed with twogussets 534 and a single gusset 536. Gussets 534 are symmetricallylocated around the longitudinal axis of the upper plate 504. The gussets534 are located in the lateral slice section of the upper plate 504 thathas greatest width along the plate. Each gusset 534 is locatedimmediately inside the outer perimeter section of the upper plate 504that transitions into lip 526. The gussets 534 are oval shaped.

Upper plate 504 is formed so that gusset 536 is centered and extendsalong the longitudinal axis of the plate. Gusset 536 extends from aposition slightly proximal to the proximal ends of gussets 534 to aposition approximately equal to the proximal ends of below discussedopenings 539. The upper plate 504 is shaped so that, adjacent gussets534, gusset 536 has a relatively wide depth. Forward of the proximal endof the gusset 536, a key hole shaped opening 538 is formed in gusset536. Opening 538 is identical in size and is positioned to be alignedwith lower plate opening 516. Distally forward of opening 538, the upperplate 504 is formed so that gusset 536 has a constant, narrow width.

A pair of additional oval-shaped openings 539 extends through the distalend of the upper plate 504. Each opening 539 has the same shape and isaligned with a complementary underling lower plate opening 520. Forwardof openings 520, upper plate 504 is further formed to have atriangularly shaped gusset 540. Gusset 540 is centered on thelongitudinal center line of the top plate. Gusset 540 is furtherpositioned to extend from an interior surface of the top plate withinthe area of the surface that is subtended by the blade head base 496.

Drive rods 74 are disposed between the blade bar lower and upper plates502 and 504, respectively. Each drive rod 74 is in the form of anelongated flat strip of metal. The drive rods 74 are formed so that, atthe proximal end of each rod, there is a circular foot 544. Each foot544 is formed to have a center located through hole 546. Through holes546 are dimensioned so that the associated drive rod feet 544 can befitted over the oscillating head drive pins 72.

While not seen in the Figures, each drive rod 74 may be shaped to form areinforcing ring around the lower and upper faces of the drive rod foot544 that defines the hole 546. In some versions of the invention, thebasic thickness of the drive rod is approximately 0.015 inches; thereinforcing rings around the hole 546 provide this section with the rodwith a thickness of approximately 0.045 inches. In some versions of theinvention, the drive rod 74 is so shaped by the selectively grinding ofthe workpiece from which the drive rod is formed.

Blade head base 496 is dimensioned to oscillate in the gap between lowerand upper plates 502 and 504, respectively. In one version of theinvention, the blade head base has a thickness approximately 0.001inches less than the width of the gap between the opposed faces of thelower and upper plates 502 and 504, respectively. Blade head base 496 isshaped so to have a relatively wide proximal end. The proximal end isfurther formed to have, adjacent each side edge a foot 548. Each foot548 is arcuately shaped. Diametrically opposed through holes 550 arefurther formed in blade head base 496 immediately forward of theproximal end. Each through hole 550 is centered on axis around which theadjacent foot 548 is centered. The distal end of the blade head base 496blade head base is further formed to define a concave semi-circularnotch 552. Notch 552 is centered along the longitudinal axis of theblade head 76. More particularly, notch 552 is dimensioned so that whenblade 52 is assembled, lower plate boss 518 seats in the notch and bladehead 76 is able to pivot around the boss.

Forward of the proximal end, the blade head base 496 has two side edges(not identified) that, extending distally along the blade head, taperinwardly. The side edges define laterally opposed notches 554. Notches554 function as the void spaces in which the opposed the forwardmosttabs 521 seat when the blade head 76 oscillates. Blade head base 496 isfurther formed to define a through window 556. Window 556 is positionedso that when the blade 52 is assembled, upper plate gusset 540 extendsthrough the window.

The blade head crown 498 has a thickness greater than that of theassociated base 496. More particularly the blade head crown is formed sothat the kerf cut by the blade head is sufficiently wide to allow theinsertion of the blade bar 494 into the kerf. The exact geometry of theblade head crown 498 is a function of the particular kerf geometry andnot otherwise relevant to this invention.

Fingers 558 and pins 560 pivotally hold the blade head 76 to the driverods 74. A pair of fingers 558 is welded over the opposed distal endsurfaces of each drive rod 74. Fingers 558 are welded to each drive rod74 so that one finger is attached to and extends forward from eachsurface. Thus, the individual fingers 558 of each pair of fingersoverlap. Each finger 558 is formed with a hole 562. Finger holes 562 areformed so that the holes of each pair of fingers overlap in the sectionof the fingers that extend forward beyond the drive rods 74.

Blade head 76 is fitted to the rest of the blade assembly 52 so thateach base foot 548 is seated in the gap between a separate pair offingers 558. When the blade head 76 is so positioned, each blade headhole 550 aligns with a separate pair of finger holes 562. A pin 560 isfitted in each set of aligned blade head and finger holes 550 and 562,respectively, to hold the blade head to the associated drive rod 74.Each pin 560 is welded or otherwise secured to the opposed finger holes562 in which the pin is seated.

Once the blade head and drive rod sub-assembly is fabricated, this subassembly is placed against the inner surface of the upper plate 504. Thelower plate 502 is fitted within the upper plate lip 526. As a result ofthis arrangement, the reinforced rings at the proximal end of the driverods seat in lower and upper plate openings 512 and 528, respectively.Fingers 558 and pins 560 seat in lower and upper plate openings 520 and539.

Once the lower bar 502 is fitted over the upper bar, the outer perimeterof the lower bar 502 is spot welded to the adjacent upper bar lip 526.This spot welding generally occurs around the outer perimeter of thelower bar. There is no spot welding adjacent the lower bar tabs 521.Thus, windows (not identified) are formed in the blade bar 494 betweeneach lower bar tab 521 and upper bar lip 526. Once spot welding iscomplete, projection welding is employed to weld boss 518 to theadjacent inner surface of the upper plate 504. Projection welding isalso used to weld gussets 536 and 540 to the adjacent inner surface ofthe lower plate 502.

V. Use of Saw

Saw 50 of this invention is prepared for use by first indexing,rotating, the head 68 so that it will be in an angular orientationrelative to the longitudinal axis of the saw barrel section 56 that ismost ergonomic for the procedure to be performed. To index saw head 68,button 232 is depressed. The depression of button 232 overcomes theforce of spring 234 and forces lock link 224 inwardly. The inwardmovement of the lock link 224 retracts tongue 228 out of the raceopening 210 in which the tongue is seated. As a result of thisdisplacement, saw head 68 is freely rotatable relative to the motorhousing 80. It should be appreciated that when the indexing lockassembly is in this state, the release state, the free end of lock linktongue 228 is disposed within saw head opening 130. This prevents thelock link 224 from laterally shifting position.

Once the saw head 68 is in the selected angular orientation, the manualforce imposed on the lock link 224 through button 232 is released.Spring 234 pushes the lock link 224 laterally outwardly relative to thelongitudinal axis of the saw head 68. Consequently, the force imposed byspring 234 causes the lock link tongue 228 to extend through the sawhead opening 130 and seat in the adjacent race opening 210. Thisreseating of the lock link tongue 228 locks the saw head 68 in the newfixed angular orientation around the center axis of the motor housing80.

Assuming that the blade coupling assembly is in the load state, a bladeassembly 52 is then coupled to the saw head 68. This process starts withthe position of the blade assembly 52 over the saw head top surface topsurface 138 so that drive head pins 72 seat in the proximal locatedholes 546 formed in the drive rods 74 and the neck of the coupling rodneck 440 seats in the wide diameter section of blade bar openings 516and 536. At this time, the proximal end of the blade bar 494 is disposedover the saw head brackets 146 and 148.

Blade assembly 52 is manually pulled distally forward. This force istransferred through the oscillating head drive head pins 72 to the othercomponents internal to the saw head 68, namely, the rear and front innerhousings 268 and 310, respectively, and the components attached to thesehousings. This force overcomes the force spring 422 imposes on the fronthousing 310 that holds it in the proximal position. Blade assembly 52 ispulled forward, until the proximal end edge surfaces of the blade bar494 is forward of the saw head brackets 146 and 148. Once the bladeassembly 52 is in this position the proximal end of the blade bar 494 ispushed down against the saw head top surface 138. The manual forwardpulling force on the blade assembly 52 is released. Once the manualforce is released, spring 422 pushes front inner housing 310 andcomponents attached thereto rearwardly. These components include thepins 72 integral with oscillating head 70. This rearward movement of thedrive pins 72 causes a like displacement of the blade assembly 52. Thisproximal movement of the blade assembly draws the proximal endlongitudinal side surfaces of the blade bar 496 against the saw headbrackets 146 and 148. The rearward displacement of the blade assembly 52also causes the blade bar 496 to move so that the bar portion thatdefines the narrow width portions of the bar openings 516 and 536 seataround the coupling rod neck 440.

The blade coupling assembly is then actuated to releasably clamp, lock,the blade assembly 52 to the saw head 68. This action is performed byrotating the wing nut 448 so that the nut bar 452 is longitudinallyparallel with the longitudinal axis of the saw head 68. As a consequenceof this motion, wing nut boss 454 and tabs 460 rotate around both thecoupling rod 428 and the cam 474. More particularly, tabs 460 areinitially disposed in the individual notches 480 defined by the cam 474.The tabs 460 move against the cam sloping walls 486. This action urgescam 474 upward relative to the saw head 68. As a consequence of beingforced upwardly, the upwardly directed exposed arcuate faces of the camhead 478 are pushed against the adjacent downwardly directed surface ofthe inner housing nose 342 as seen in FIG. 44. The continued upwardmotion of the cam 474 causes the cam to flex the inner housing noseupwardly. Eventually this action causes the opposed nose side edges 346to press against the adjacent inner circular wall of the saw head thatdefines saw head bore 166. This action locks the front inner housing 310and components attached thereto against rotation relative to thelongitudinal axis of the saw head 68.

The abutment of the front inner housing nose 342 against an inner wallof the saw housing 68 also prevents further upwardly movement of the cam474. Wing nut tabs 460 continue to rotate along the cam sloping wall486. As a result of this continued movement of the wing nut 448, thewing nut is forced downwardly, away from the front inner housing nose342. The downward movement of wing nut 448 results in a like downwarddisplacement of the Bellville washers 470 located internal to the wingnut. The movement of the Bellville washers 470 causes the washers toincrease the force they impose of on the wing nut retainer 450. Thisforce is greater than the opposite force spring 446 imposes on thecoupling rod-wing nut retainer sub-assembly. Thus, the downward movementof the Bellville washers 470 urges the coupling rod and wing nutretaining sub-assembly in a like downward motion. The downward movementof coupling rod 428 results in the pressing of the undersurface of therod head 442 against the adjacent exposed face of the blade bar upperplate that defines opening 538. Once the rotation of the wing nut 448results in wing nut tabs 460 seating in notches 490, the couplingassembly is locked in the run state, no further force is needed to holdthe wing nut so that the coupling assembly holds the blade assembly 52to the saw 50.

Once blade assembly 52 is in the locked in position, saw 50 is ready foruse. The depression of the trigger 66 results in the actuation of themotor 66. The rotational moment of the motor rotor 68 is transferredthrough the drive coupler 296 to the output shaft 240. Due to the shapeof the drive coupler 296, the output shaft 240 remains rotatablyconnected to the motor rotor 68 as the output shaft is pulled forward inorder to attach the blade assembly 52.

The rotation of the output shaft 240 results in the off center rotationof the shaft head 256 and nose 264, respectively. The coupling of thewobble ring 406 to the oscillating shaft 242 prevents the wobble ringfrom rotating. Consequently, as a result of the rotation of shaft head256, the wobble ring head 414 oscillates back and forth in an arcuatepath of travel. The motion is captured by the oscillating shaft centersection 352. Oscillating shaft 242 is thus forced into a oscillatingmotion. The oscillating motion of shaft 242 is output by the oscillatinghead pins 72 as reciprocal motion.

The reciprocal motion of the oscillating head pins 72 is transferred tothe blade assembly drive rods 74. The reciprocation of the drive rods74, in turn, causes the blade head 76 to pivot about boss 518. Thepivotal movement of the blade head 76 enables the blade head to cut thetissue to which the head is applied.

During the course of using saw 50 and blade assembly 52 of thisinvention. Small bits of severed tissue may enter the open distal end ofthe blade bar 496. These debris may enter the small spaces between theface of the blade head base 496 and the adjacent inner surface of thelower or upper bar 502 or 504, respectively. In the event tissue becomesentrained in this space, it will migrate into the moving space of window556. From window 556, the debris are discharged out of the blade barthrough the lower plate discharge ports 522.

Saw 50 and saw blade 52 of this invention are constructed so that onlycomponent that oscillates is the distally located blade head 76. Thus,the system of this invention has the benefits provided by other sagittalsaw assemblies where only a relatively short length blade head locateddistally forward of the saw head 68 pivots.

The saw 50 of this invention is further constructed so that the saw head68 is able to index relative to the saw housing 54. The indexingassembly is constructed so that a first biasing member, wave spring 181,holds the saw head 68 and components internal to the saw head to themotor housing 80 while a second biasing member, spring 234, holds thesaw head in a locked index state. Consequently, when surgical personnelreset the index position of the saw head 68 only a first minor force,the force exerted by spring 234, needs to exerted in order to unlock thesaw head from the lock state so it can be rotated. Surgical personnelthus do not have to apply significant force, in order to overcome asingle biasing member that both holds the saw head in fixed longitudinalposition and prevents head rotation.

The coupling assembly of the saw of this invention to make it relativelysimple to both remove and attach new blades to the saw head 68. Itshould further be appreciated that the coupling assembly is keyless. Onedoes not require an additional tool separate from the saw that needs tobe sterilized and accounted for when in the operating room.

It should be appreciated that gussets 536 and 550, since they extendbetween the lower and upper plates 502 and 504 respectively, providestructural strength to the blade bar 496. This strength prevents theblade bar from flexing when exposed to unbalanced top and bottomloading.

Still another feature of the blade assembly of this invention is thedischarge ports 522 located in the distal section of the blade bar 494,the section in which the blade head is seated. Discharge ports 522provide a discharge path through which cut tissue and other debrisentrained in the blade bar 494 are ejected from the blade 52. Thisprevents this material from being trapped in the blade where it canimpede the movement of the blade head and/or stress the components ofthe blade assembly to a level at which there is the potential forcomponent failure.

VI. Alternative Embodiments

It should be recognized that the above description is directed to aspecific version of the saw 50 and blade assembly 52 of this invention.Other versions of the invention may have features and benefits differentfrom what has been described.

FIGS. 45 and 46 are overviews of an alternative saw head assembly ofthis invention. This saw head assembly includes a saw head 68 a in whicha single inner housing 570 is rotatably mounted.

Turning to FIGS. 47, 48 and 49, it can be seen that saw head 68 a hasthe same basic proximal end section 124, tapered section 126, firstintermediate section 128 and distal end section 136 of the firstdescribed saw head 68, (FIGS. 7 and 8). Saw head 68 a also has thepreviously described openings 130, 135, 172 and 174 and bores 133, 160,162, 164, 166, 168, 176 and 178 of saw head 68. Saw head 68 a has adistal end portion 136 a that is slightly different than the similarportion 136 of saw head 68. Specifically, distal end portion 136 a isformed with an opening 576 into bore 164. Opening 576 is concentric withopening 174.

Saw head 68 a has a top surface 138 a with the same basic geometricprofile of top surface 138 of saw head 68. Only a single pair ofbrackets 578 extend upwardly from the top of the saw head 68 a topartially extend over the proximal end of the top surface 138 a. Eachbracket 578 has a wall 579 that extends upwardly from the associatedside of the saw head 68 a that runs along the outwardly taperingproximal side edge of the top surface 138 a. A rectangular step 580extends along the corner where the saw head top surface 138 a and thebracket side wall 579 meet. A tab 582 extends perpendicularly inwardlyfrom the top of the side wall 579. Each tab 582 extends both over theunderlying step 580 and a short distance over the saw head top surface138 a. Brackets 578 are further formed so that tabs 582 only subtendportions of the top surface 138 a immediately forward of the proximalend of the top surface.

Inner housing 570 substitutes for the combined front and rear innerhousings of the first embodiment of the invention. The inner housing570, best seen in FIGS. 50, 51 and 52 is formed with first, second andthird bores 592, 594 and 596, respectively, that extend coaxiallyforward from the proximal end of the housing. Bore 592 forms theproximal end opening into the inner housing. Bore 594, which isimmediately forward of bore 592, has a diameter slightly less than thatof bore 592. It should further be appreciated that the section of theinner wall of the inner housing 570 that defines the distal end of bore592 is formed with threading (not identified). Also not identified isthe cut out present for manufacturing purposes between the threadeddistal end of the first bore 592 and the second bore 594.

Third bore 596 is located forward of second bore 594. The third bore 596has a diameter slightly greater than that of second bore 594. The innerhousing 570 is further formed to define an annular, inwardly extendinglip 602. Lip 602 is located between the second and third bores 594 and596, respectively, so as to define the distal end base of the secondbore 594. Inner housing 570 is further formed to have side window 604.Window 604 extends laterally through the inner housing. Internal to theinner housing, side window 604 is defined by two planar parallel spacedapart interior walls. The side window is primarily located forward ofthird bore 596. However, it should be further appreciated that sidewindow 604 also intersects both the whole of third bore 596, the voidspace defined by lip 602 and the distal portion of the second bore 594adjacent the lip.

Inner housing 570 is further formed to have top and bottom openings 330a and 332 a, respectively into the third bore 596. An annular lip 599extends around the base of top opening 330 a. An annular lip 601 extendsaround the base of bottom opening 332 a. A nose 342 a extends forwardfrom the front face of the inner housing 570. A bore 338 a extendsinwardly proximal from the housing front face. The inner housing 570 isalso shaped to have two longitudinally extending diametrically opposedside windows 604 (one shown).

An output shaft 608 is rotatably disposed inside inner housing 570.Output shaft 608, now described by reference to FIGS. 53 and 54, has astem 244 a, a main section 246 a and a collar 252 a that correspond tothese features of the first described output shaft 240. Immediatelyforward of the proximal end of shaft main section 246 a, an annulargroove 609 is present in this portion of the shaft 608. Forward of thecollar 252 a, shaft 608 has a cylindrical head 610. Head 610 extendsforward from the collar 252 a along an axis parallel to and laterallyoffset from the common longitudinal axis of the shaft stem 244 a, mainsection 246 a and collar 252 a. Shaft 608 is further formed so there isan annular groove 611 in the head 610 immediately proximal to the distalend of the head.

Bearing assemblies 286 and 288 rotatably hold output shaft 608 in theinner housing second bore 594. The inner races of both bearingassemblies 286 and 288 are disposed over the shaft main section 246 a.The forward facing round face of bearing assembly 288 seats againstshaft collar 252 a. The distally directed outer face of the outer raceof bearing assembly 288 seats against inner housing interior lip 602.The distally directed outer face of the inner race of bearing assembly288 seats against the radially outwardly directed proximally facing faceof the shaft collar 252 a.

A bearing retainer 612 holds the proximal-located bearing assembly 286in the inner housing first bore 592. Best seen in FIG. 55, bearingretainer 612 is generally ring shaped. The outer circumferential wall ofthe bearing retainer 612 is provided with threading, (not illustrated).Diametrically opposed, longitudinally aligned notches 614 extendinwardly from the proximally directed annular face of the bearingretainer 612. Notches 614 are dimensioned to receive a tool (notillustrated) used to insert and remove the bearing retainer.

When this blade drive assembly is put together, the bearing retainer 612is screw fitted into the threaded section of inner housing first bore592. The retainer 612 abuts the proximally directed annular face of theouter race of bearing assembly 286. A C-shaped snap ring 609 seats inshaft groove 611. Snap ring 611 is disposed against the proximallydirected face of the inner race of bearing assembly 286 to limit forwardmovement of the output shaft 608. A washer 607 is disposed betweenbearing assembly 286 and snap ring 611.

The rotational movement of output shaft 608 is output as oscillatingmotion by an oscillating yoke 616 and oscillating head 618 coaxiallymounted to the inner housing 570 to rotate. The oscillating yoke 616,best seen in FIGS. 55 and 56, is formed from a single piece of metalshaped to have a main body 620 that is generally trapezoidal in shape.At the distal end, main body 620 is of short length; at the proximalend, longer in length. Opposed fingers 622 extend proximally rearwardlyfrom the opposed proximal end corners of the main body 620.

Yoke 616 is further formed to have a bore 624 that extends laterallythrough the main body 620, top to bottom. Bore 624 has a generally ovalshape. While the cross sectional geometry of bore 624 is constant, thebore does taper inwardly. More specifically the planar surfaces thatdefine the sides of the bore 624 taper inwardly. At the top of the mainbody 620, the distance between these surfaces is wider than at that thebottom of the main body. The curved walls that define the opposed endsof the bore have a constant radius of curvature along the length of thebore.

The oscillating head 618, now described by reference to FIGS. 58 and 59,is seated in yoke bore 624. Starting at the lower end, oscillating head618 has a cylindrically shaped foot 628. Immediately above the base ofthe foot 628, the foot is formed with groove 629 that extendscircumferentially around the foot. Located above foot 628, theoscillating head 618 has a cylindrical leg 630. Leg 630 has a largerouter diameter than foot 628. Threading is formed around the outercircumference of leg 630 (threading not illustrated.) A trunk 632extends above leg 630. Trunk 632 has a cylindrical structure. While thetrunk 632 is generally circular in shape, it is formed so as to have twodiametrically opposed flats 634. The flats 634 extend upwardly from thebottom of the trunk 632 at approximately 90% of the length of the trunk.The flats 634 taper outwardly relative to the longitudinal axis of thehead 620 when moving from bottom to top along the head.

Above the trunk 632, oscillating head 620 is formed to have a collar636. The collar 636 is cylindrical in shape and has a diameter slightlygreater than that of the adjacent portion of the trunk 632. Above collar636 oscillating head 620 has a neck 640. The neck 640 is cylindrical inshape and has a diameter greater than that of the collar 636. A smallstep 638 is located around and below the base of the neck 640. Step 638thus surrounds the top of the collar 636.

A top plate 642 similar to top plate 370 (FIG. 28) projects outwardlybeyond oscillating head neck 640. Drive pins 72 extend upwardly fromholes 644 in the opposed ends of the drive plate. In FIG. 58 a brazering 646 is located in the base of each hole 644. The braze rings 646become dispersed in the brazing process so as to secure the drive pins72 to the oscillating head 618.

A bore having a plurality of different sections extends axially throughthe oscillating head 620 from the foot 628 to the neck 640. The bore hasa first section 648 that extends through the foot 628, leg 630 and trunk632. A second section 652 has a wider diameter than the first section648 extends through the collar 636 and into the base of the head.Between the first and second bore sections 648 and 652, respectively,there is a tapered transition section 650. Above the second section 652,the bore has a third section 654 that opens out into the top plate 642.The top of the oscillating head collar 636 that defines the bore thirdsection 654 is provided with threading (not illustrated). Not identifiedis the tapered transition section between the second and third sections652 and 654, respectively.

When saw head 68 a is assembled, the oscillating head 618 is fitted inthe yoke bore 624 so that trunk 632 is seated in the yoke bore. A nut660, seen best in FIGS. 60 and 60 a, is threaded over the oscillatinghead leg 630 to hold the head 618 in the yoke bore 624. Nut 660 whilegenerally circular, is shaped to have a washer shaped head 661 fromwhich a base 662 extends. While base 662 is generally circular in shape,it is formed with two opposed flats 663 (one shown). The flats 663receive a tool for fastening and loosening the nut 660.

When the saw head is assembled, the nut head 661 abuts the yoke 618. Nut660 thus presses the yoke 618 upwardly so that the inner walls thatdefine the tapered sides of bore 624 press against the tapered headflats 634. A torque wrench is used in this process to ensure that theyoke 616 is not over compressed around the oscillating head 618.

Owing to the compression of the yoke 616 around the oscillating head618, these components, for practical purposes, are a single unit. Thus,when the saw is actuated the oscillating head does not move relative tothe yoke. Also, since a torque wrench is used to fit nut 660 in place,the amount of outward expansion stress to which the material definingthe yoke bore 624 is exposed can be set. Collectively, these featuressubstantially reduce the likelihood of the material forming the yoke 616will crack and/or suffer stress failure.

A spring biased plunger 664, described with respect to FIGS. 61 and 62,is disposed in the oscillating head 620. The plunger 664 has a diskshaped base 666. A cylindrical stem 668 extends upwardly from base 666.

Plunger 664, when in the retracted state, is disposed in oscillatinghead second bore section 652. A washer shaped plunger retainer 670,shown in FIGS. 63 and 64, holds the plunger 664 in the oscillating headbore. While not shown it should be understood that the outer cylindricalsurface of the plunger retainer is provided with threading. Thisthreading facilitates the screw securement of the plunger retainer tothe complementary threading around the oscillating head bore thirdsection 654. The plunger retainer 670 has a center through hole 672through which the plunger stem 668 extends. A counterbore 674 opens intothrough bore 672 from the concealed face of the plunger retainer 670.Two opposed closed end bores 676 are located on opposed sides of theouter face of the plunger retainer 670. Bores 676 receive a fasteningtool that facilitates the insertion and removal of the plunger retainer670 from the oscillating head bore third section 654.

When saw head 68 a is assembled, a spring 677 is disposed in theoscillating head bore second section 652. Spring 677 extends between thestatic surface of the oscillating head that defines the bore taperedsection 650 and the plunger base 666. The spring 677 thus pushes theplunger outwardly so the plunger stem 668, if unopposed, projects abovethe oscillating head top plate 642. Thus, during removal of the sawblade 702 (FIG. 65) plunger 664 exerts an upward force on the blade barto force the bar away from the saw head 68 a.

When the plunger 664 is so extended the plunger head 668 seats againstthe annular step between the bore 672 and counterbore 674 internal tothe retainer 670. Thus, retainer 670 holds the plunger to theoscillating head 618.

Oscillating head 618 extends through the inner housing top opening 330a, window 604 and the bottom opening 332 a. In the top opening 330 a, abearing assembly 682 rotatably holds the oscillating head 618 in place.More particularly, bearing assembly 682 extends between the innercylindrical wall of the inner housing 570 that defines opening 330 a andoscillating head collar 636. The bottom surface of the outer race of thebearing assembly 682 rests on the annular lip 599 that defines the baseof opening 330 a.

Foot 628 is the portion of oscillating head 618 that is disposed ininner housing bottom opening 332 a. A bearing assembly 684 rotatablyholds the oscillating head foot 628 to the inner housing. Moreparticularly, bearing assembly 684 extends between the internalcylindrical wall of the inner housing 570 that defines the bottomopening 332 a and the oscillating head foot 628. The upwardly directedface of the outer race of the bearing assembly 684 presses against lip601 that defines the base of the bottom opening 332 a. A snap ring 688disposed around the end of the foot 628 holds the bearing assembly 684to the oscillating head. Snap ring 688 is seated in annular groove 629formed in the foot 628. A washer 686 is disposed between the inner raceof bearing assembly 684 and snap ring 688.

For purposes of assembly and disassembly, oscillating head 618 isaccessible through saw head opening 576. A plug 690 removably coversopening 576.

A bearing assembly 694 is disposed over the head 610 of the output shaft608. A snap ring 696 seated in shaft groove 611 holds the bearingassembly 694 to the shaft head 610. It will further be appreciated thatbearing assembly 694 is formed to have an outer race with a crosssectional profile equal to that of a center slice through a sphere. Aspacer (not identified) is located on either side of the inner race ofbearing assembly 694.

Bearing assembly 694 is positioned so as to be disposed within theopposed fingers 622 of oscillating yoke 616. More particularly, theouter race of the bearing assembly 694 bears against the opposed planarsurfaces of the yoke fingers 622. Thus, the rotation of the output shaft608 is transferred by the bearing assembly 694 into a motion that causesyoke 618 and, by extension, oscillating head 618 to oscillate.

FIG. 65 illustrates a blade assembly 702 designed for use with saw head68 a. Blade assembly 702 has a blade bar 494 a from which a moveableblade head 76 a extends. The blade head 76 a is generally the same shapeas the initially described blade head 76. However blade head 76 a hasbase 496 a with contiguous proximal and distal sections 704 and 706,respectively. The proximal section 704 is the portion of the blade base496 a in which openings 548 and notch 552 are formed. Forward of theportion of the proximal section 704 through which openings 548 areformed, the section tapers inwardly. The base distal section 706 extendsout forward and laterally beyond the relatively narrow most forwardportion of the proximal section 704. Window 556 is formed in the bladebase distal section 706. The teeth defining crown 498 of the blade head76 a extends forward from the base distal section 706.

Blade bar 494 a is formed from lower and upper plates 502 a and 504 a,respectively. Plates 502 a and 504 are generally similarly to theinitially described plates 502 and 504. However, at the proximal end ofthe blade bar 494 a, the plates do not have indentations similar to thepreviously described indentations 508 (FIG. 43).

At the distal end of the blade bar 494 a, plates 502 a and 504 a areformed to have oval shaped openings 708 and 710, respectively. Eachplate 502 a and 504 a has two rows of linearly aligned openings. Theopenings 708 and 710 are located immediately inward of the longitudinalside edges of the plates 502 a, 504 a, forward of openings 520 a and 539a, respectively. In one version of the invention, plates 502 a and 504 aare formed so that, when assembled together, openings 708 and 710 arenot in registration. This is to facilitate final manufacture of bladeassembly 702. Specifically, at this time, the upper plate 504 a ispositioned on a fixture so its inner surface is facing upwardly, isexposed. More particularly the fixture has fingers that extent throughthe upper plate openings 710. Once all the other components areassembled in the upper plate 504 a, the lower plate 502 a is placed overthe upper plate 504 a. Since openings 708 are not in registration withthe upper plate openings 710, the fixture fingers abut the inner surfaceof the lower plate 502 a. Thus during the welding process used to securethe plates 502 a and 504 a together, the fingers hold the distal end ofplate 502 a off the underlying plate 504 a.

During use actuation of the blade assembly 702, windows 708 and 710function as ports through which bone chips and other matter entrained inthe distal open end of the blade bar 494 a is ejected from the bladebar.

Blade assembly 702 includes drive rods 74 a. D Each drive rod 74 a isshaped so that the opposed fingers 558 a are integrally formed with thedrive rod. Specifically, the drive rod is surface ground to form thenarrow thickness elongated body and a relatively wider distal end. Acutting process such as a wire electrical discharge machining process isused to form the finger-separating kerf in which the blade head base 496a is slip fitted. During the surface grinding process, each drive rod 74a is further formed so that the proximal end foot 544 has a greaterthickness than the distally adjacent elongated body.

Blade assembly 702 is fitted to saw head 68 a in a manner similar tothat in which blade assembly 52 is fitted to saw head 68. The proximalend of the blade bar seats between the steps 580 integral with brackets578. It should be appreciated that blade assembly 702 is relativelythin. This facilitates the insertion of the blade assembly in the narrowslots of a cutting guide (jigs) used to position the blade to ensure theblade makes an appropriately shaped cut. In many versions of theinvention, the bar of the blade assembly has an overall thickness ofless than 0.080 inches. In some preferred versions of the invention thisthickness is 0.065 inches or less. In still other preferred versions ofthe invention, this thickness is 0.055 inches or less. It is furtherunderstood that the thickness of the teeth that extend forward from theblade head should be marginally greater than the width of the blade bar.A minimal difference in these two dimensions is 0.001 inches. Therelative dimensions of these components substantially eliminates thelikelihood the blade bar will become lodged in the kerf formed in thetissue.

Also, as soon as the blade assembly 702 is pulled beyond tabs 582, theforce of the plunger 664 and spring 696 pushes proximal end of the bladebar 494 a off the saw head top surface 138 a. This further reduces theeffort required to remove the blade assembly 702.

From FIG. 65 it can further be seen that blade head crown 498 a isformed with laterally side edges 714 that are tapered. More specificallythe side edges 714 are tapered so that going forward, distally, alongthe crow, the edges taper outwardly. The opposed ends of the base of thecrown 498 a are each provided with a laterally extending finger 718.These structural features are provided so that the longitudinal sideedges of the crown 498 a proximal to the teeth function as plows. Theseplows push debris laterally away from the crown 498 a. This debrisdisplacement reduces the volume of the debris that then become entrainedin the blade bar.

FIG. 66 illustrates an alternative oscillating yoke 730 that can beemployed with saw head 68 a. Yoke 730 is formed to have a U-shaped mainbody 732. More particularly, the yoke main body 732 is further formed soas to have an inner, U-shaped wall with two parallel spaced apartsurfaces 734. Below the base of the center of the base of the main body732, yoke 730 is further formed to have a circular boss 736. A threadedbore 738 (shown in phantom) extends upwardly through boss 736 partiallyinto the main body. A smooth walled counterbore 740 extends coaxiallyupward from bore 738 through the rest of the yoke main body 732.

Oscillating yoke 730 is further formed to have two longitudinallydiametrically opposed generally U-shaped notches 744. Notches 744 arelocated in the top of the yoke main body 732 such that each notch opensinto counterbore 740.

An oscillating head 746, shown in detain in FIG. 67, is attached to andextends above oscillating yoke 730. Oscillating head 746 is generallysimilar in design to the previously described oscillating head 70. Thus,oscillating head 746 includes a top plate 370 b from which two drivepins 72 b extend. A multi-section boss 374 b extends below the top plate370 b. Two opposed feet 382 b project below the bottom face of boss 374b. A set of bores (not identified) extend through the components formingthe oscillating head 746.

Oscillating yoke boss 736 is rotatably mounted in inner housing bore 332a. Oscillating head boss 374 a is rotatably mounted in inner housingbore 330 a. When the blade drive assembly is so assembled, feet 382 aintegral with head 746 seat in yoke notches 744. A retaining screw 750holds the oscillating head 746 to the oscillating yoke 730. As seen inFIG. 68, retaining screw 750 has a cylindrical, bottom located stem 752.The outer surface of stem 752 is formed with threading (not illustrated)designed to engage the threading of oscillating yoke bore 738. Abovestem 752, retaining screw 750 has a smooth walled main body 754 and ahead 756. Head 756 has a diameter larger than that of the main body 754.Notches 758 extend inwardly from the outer perimeter of the head toreceive a fastening/removal tool (not illustrated).

When the components forming the drive assembly are put together, thescrew main body 754 extends through counterbore 740 of the oscillatingyoke 730. Screw stem 752 is screw fitted in the top of yoke bore 738.The head 756 of the retaining screw 750 thus bears against the annularinternal step into which oscillating head bore 384 a opens. Screw 750 isfitted into the open bottom end of oscillating yoke bore 738.

When yoke 730 and oscillating head 746 are fitted to saw head 68 abearing assembly 654 is positioned so as to be disposed within theopposed fingers of the yoke. More particularly, the outer race of thebearing assembly 630 bears against the opposed planar surfaces 734 ofthe yoke 730. Thus, the rotation of the output shaft 584 is transferredby the bearing assembly 630 into a motion that causes yoke 730 and, byextension, head 746 to oscillate.

FIG. 69 is an exploded view of an alternative blade assembly 52 aconstructed in accordance with this invention. Blade assembly 52 a hasthe same basic structural components as the first described bladeassembly 52. Blade assembly 52 a is also provided with an RFID tag 770best seen in FIG. 70. The RFID tag 770 is encased within a plastic block772. Also disposed within block 772 is a coil 774 represented by thecross section of a single wire. Coil 774 is connected to the RFID andfunctions as the component through which signals are exchanged with theRFID.

Block 772 is mounted to the blade bar of blade assembly 52 a. Moreparticularly, blade assembly 52 a includes lower and upper plates 502 aand 504 a which are generally similar in structure to the firstdescribed blade bar-forming plates 502 and 504. Lower plate 502 a isfurther formed to have a distal end through window 776. Upper plate 504is formed to have a distal end through window 778. Plates 502 a and 504a are formed so that when they are assembled together to form the bladebar, windows 776 and 778 are in registration. When the componentsforming blade assembly 52 a are assembled together, block 772 is mountedin plate windows 776 and 778.

In some versions of the invention, block 772 is formed so as to have aflange or lip that extends outwardly from the lateral side walls of theblock. This flange has a depth less than that of the block 772. Theflange seats in the interstitial space between the opposed, inwardlydirected faces of the plates 520 a and 504 that define the perimeters ofwindows 776 and 778, respectively. The flange thus holds block 772 tothe blade bar.

FIG. 56 illustrates the saw 50 a with which blade assembly 52 a is used.Saw 50 a contains the same basic components of the first described saw50. Saw head 68 a of saw 50 a is further provided with a coil 782positioned to inductively exchange signals with blade assembly coil 774.More particularly, coil 782 is mounted to the saw head 68 a so as to bein a plane parallel and slightly below the head top surface 138 a. Coil782 is located below the top surface section 144 a. The coil 782 isdisposed in a block 784 an outer face of which forms a portion of topsurface section 144 a. In some versions of the invention, block 784 isformed from plastic that can withstand the rigors of autoclavesterilization. In other versions of the invention, block 784 is metal.

Coil 782 is connected by conductors 792 to a coil 788. Coil 788 isdisposed around the saw head proximal end section 124 a. Moreparticularly, coil 788 is encased in a ring 790 fitted disposed aroundthe saw head proximal end section 124 a. The ring 790 is seated in agroove formed in the saw head proximal end section 124 (groove notidentified). The outer surface of ring 790 is flush with the adjacentouter surface of the saw head proximal end section 124 a.

Conductors 792, for the purposes of illustration, are shown as spacedinwardly from the saw head intermediate sections 128 a and 132 a. Insome versions of the invention, conductors 792 are disposed against theinner wall of the saw head 68 a. In other versions of the invention,conductors 792 are seated in a groove or a bore that extendslongitudinally through the saw head 68 a.

Integral with the motor housing 80 a is a coil 794 that surrounds coil788. Coil 794 is contained in a ring 796. The ring 796 is seated in agroove formed in the inner wall of housing 80 a that defines the housingthird bore (groove not identified).

As seen in FIG. 57, coil 794 is connected to an RFID transceiver 798internal to the saw 50 a. As described in the Applicant's Assignees'U.S. Patent Application No. 60/694,592, POWERED SURGICAL TOOL WITHSEALED CONTROL MODULE, filed 28 Jun. 2005 the contents of which arepublished in US Pat. Pub. No. 2007/0085496 A1, now U.S. Pat. No.7,638,958, the contents of which is incorporated herein by reference, itis known to provide a powered surgical tool with a processor 802 capableof regulating the operation of the tool. A data transceiver internal tothe tool reads data used to regulate tool operation. RFID transceiver798 integral with saw of this invention functions as such a datatransceiver.

It should be appreciated that when RFID transceiver outputs signals tothe RFID tag 770, the signals are first inductively transferred fromcoil 794 to coil 788. The signals are then inductively transferred fromcoil 782 to blade assembly coil 774 from where they are forwarded to theRFID tag 770. Signals generated by the RFID tag 770 for the saw RFIDtransceiver 798 are forwarded to the transceiver over the reverse path.

Static coil 794 surrounds saw head coil 788. Therefore, there is alwaysinductive signal exchange between coils 788 and 794 independent of theindex position of the saw head 68 a.

Internal to the blade assembly RFID tag 770 is a memory represented byblock 806 of FIG. 58. The RFID memory contains data that identifies theblade assembly 52 a. For example, in a blade length field 808 data arestored that indicates this length of the blade assembly 52 a. In someversions of this invention, this length is the longitudinal distancealong the blade from the center of the drive rod foot hole 546 to theapex of the blade head crown 498 when the blade head is centered on theblade bar. One or mode blade geometry data fields 810 contain data thatdescribes the profile of the blade head crown. These data describe: theradius of curvature of the crown; the arc subtended by the distal end ofthe crown; and the thickness of the crown. A teeth geometry data field811 contains data that describes the profile of the teeth formed in theblade crown.

The RFID tag memory also contains data that are used to regulate theactuation of the blade assembly 52 a. These data are, for example,stored in a default and maximum operating speed data fields 812 and 814.The data in the default operating speed field 812 indicates a standardinitial cycle rate at which the blade head should be oscillated back andforth. The data in the maximum operating speed data field 814 containsdata indicating the maximum speed at which the blade head should beoscillated.

The RFID tag memory also contains fields in which data are written afterthe blade assembly 52 a is attached to the saw. A use history data field816 is used to store data indicating if the blade assembly has been usedand/or the number of times the blade assembly has been used. In someversions of the invention, the use history data field 816 may be asingle bit flag field. There is also a time stamp field. The time stampfield 818 is used to store data indicating the first or last time theblade assembly 52 a was attached to a saw.

When saw 50 a and blade assembly 52 a of this version of the inventionare used, the blade assembly is attached to the saw head 68 a is in thefirst described embodiment. The data in the RFID tag 770 are read more.More particularly, the RFID transceiver 798 integral with the saw 50 aperiodically generates a basic interrogation signal, step 822 of FIG.74. This signal is continually periodically output by transceiver 798.If a blade assembly 52 a is not attached to the saw 50 a, there is noresponse to this signal.

When a blade assembly 52 a with an RFID tag 770 is attached to the sawhead 68 b, in response to the basic interrogation signal, the RFID tagoutputs a short acknowledgment signal, step 823. Upon receipt of thisacknowledgement signal, the RFID transceiver 798 outputs a read datarequest to the RFID tag 770, step 824. In response to this request, instep 713, the RFID tag 770 outputs all the stored data to the RFIDtransceiver 798, step 825. The RFID transceiver, in turn, forwards thedata to the saw processor 802, step 826. Saw processor 802 thenregulates the actuation of the saw based on these data.

Saw processor 802 may also cause the data describing the characteristicsof the blade assembly 52 a to be forwarded to a remote unit through asecond transceiver 828. These data are then received by other equipmentin the operating room in which the surgical procedure in which saw 50 aand blade assembly 52 a are being used.

One such piece of equipment is a surgical navigation system. Thissystem, as generally illustrated in FIG. 75 includes a number oftrackers 830 a and 830 b. Each tracker 830 a and 830 b is attached to aseparate one of the surgical tools; tracker 830 a is attached to saw 50a. A localizer 838 receives signals emitted by the trackers 830 andgenerates basic signals based on the position and orientation of eachtracker 830 a and 830 b. The localizer generated signals are forwardedto a navigation processor 840. The navigation processor 840, based onthe localizer-generated signals, determines the position and orientationof the surgical tools to which the trackers 830 a and 830 b areattached. Based on these data, an image is generated indicating theposition and orientation of the surgical tools relative to the surgicalsite.

As indicated in step 832 of FIG. 76, in a method of surgical navigationusing saw 50 a of this invention, based on signals emitted by tracker830 a, the position and orientation of saw 50 a is determined. In Afterthe saw head 68 a is indexed, (step not shown,) blade assembly 52 a ismounted to saw 50 a, step 834.

Then, in a step 836 a surgical tool known is a pointer 837 is touched toa reference point or points formed on the blade bar. These points may beone or more divots 842 (one shown) or a groove formed on the blade bar.A separate tracker, tracker 830 b, is attached to pointer 837.Therefore, as a consequence of the execution of step 836, navigationprocessor 840 generates data indicating the position and orientation ofthe blade bar head reference point(s). The navigation processor 840therefore has data indicating both the position and orientation of thesaw 50 a and of the reference point(s). Based on these data, in a step844, the navigation processor 840 determines the angular orientation,the index position, of the blade assembly 52 a.

In a step 846, the data in the blade assembly RFID tag 680 are read. Ina step 848 at least the data descriptive of blade length and crowngeometry are forwarded to the navigation processor 840. Owing to theproximally-directed biasing force imposed by spring 422 on the bladeassembly 52 a, the proximal ends of the blade bar 496 regularly seat ina known position relative to a fixed reference point on the blade headtop surface. Thus, the navigation processor 840 contains the followingdata: the position and orientation of the saw 50 a; the angularorientation of the blade bar around a known axis of the saw; and thelength of the blade assembly 52 a. Based on these data, in step 850, thenavigation processor generates data indicating the position andorientation of the distal end of the blade assembly 52 a, crown 498. Thenavigation processor 840 is then able to generate an image on a display852 indicating the position of the blade assembly crown 498 relative tothe surgical site on the patient.

In an alternative version of the method of the invention, after the sawhead 68 a is indexed, pointer 837 is touched to a divot 746 or otherreference marker formed on the saw head 68 a. Based on the position ofthis divot, navigation processor 840 determines the orientation, indexedposition, of the saw head 68 a. The blade bar is static relative to thesaw head. The position of the saw head 68 a is then used to determinethe index orientation of the blade assembly relative to the saw 52 a.

FIGS. 77 and 78 illustrate an alternative blade assembly 52 b. Bladeassembly 52 b has the same basic blade bar and blade head of thepreviously described blade assemblies. However, blade assembly 52 b hasa blade bar 494 b where the opposed side walls at distal end section inwhich the blade head base is seated are formed with ports 862. Ports 862are created by first forming slots (not illustrated) in the upper platelip 526. As a consequence of the attachment of the lower and upperplates 502 and 504, respectively, together, the slots become blade ports862.

While not illustrated, it should be understood that blade assembly 52 bincludes an appropriate blade head. The blade head is formed with a basefrom which fingers 868 extend outwardly from the opposed longitudinalside edges. The blade head s formed so that when the blade head pivotsback and forth, each set of fingers on one side of the head extend ashort distance through the associated blade bar side-wall located ports862.

When blade assembly 52 b of this version of the invention cuts bone orother tissue, at least some of the tissue enters the distal end openingof the bar 494 b through which blade head 76 b extends. As the bladehead pivots back and forth, the fingers force the entrained tissue outthrough the bar assembly side wall ports 862.

Moreover, the saw of this invention may be used to oscillate saw bladesthat have different structures from what has been disclosed. Forexample, in some versions of the invention, the oscillating shaft mayoscillate a single pin or a cap designed to receive the proximal end ofa conventional saw blade formed out of a single piece of metal. Inversions of the invention wherein there is a single pin, it isanticipated that the pin will have an opening with a noncircularprofile. The saw blade would have an opening with a similar profile suchthat when the blade is seated over the pin, the two components rotatetogether. If the oscillating head contains a cap, internal to the cap isan assembly for holding the blade in the cap.

There is no reason that, in all versions of the invention, theoscillating drive assembly be mounted to saw head so that theoscillating head is biased towards the proximal end of the saw head. Inalternative versions of the invention, the oscillating drive assemblymay be configured so that the biasing member normally urges the exposedoscillating head components to the forward, distal end of the saw head.

Alternative means to index the saw head relative to the rest of the sawmay be employed. For example, in some versions of the invention, thelink mechanism that controls indexing may be moveably attached to thesaw housing not the rotating saw head. In some versions of theinvention, a single biasing member may both press the saw head againstthe static saw housing and inhibit rotation of the saw head.

The blade coupling assembly may likewise vary. Thus, there is norequirement that in all versions of the invention the blade couplingassembly simultaneously function as a device that clamps the innerhousing assembly to the saw head to prevent relative motion of thesecomponents. There may be reasons in some versions of the inventionwherein removable components are used to releasably secure the bladeassembly to the saw head.

The blade assembly may similarly vary from what has been described. Forexample, in some versions of the invention, a single drive rod may beall that is needed to pivot the blade head. Similarly, alternative meansmay be employed to pivotally connect the drive rod(s) to the blade head.Alternative means may also be employed to pivotally mount the blade headto the blade assembly bar. These include the alternative assembliesemployed in the incorporated-by-reference U.S. patent application Ser.No. 10/887,642.

Further the openings in the distal section of the blade bar in which theblade head is disposed and through which entrained tissue is dischargedmay vary from what is illustrated.

Therefore, it is an object of the appended claims to cover all suchvariations and modifications that come within the true spirit and scopeof the invention.

1-20. (canceled)
 21. A method of assembling a surgical sagittal saw,said method including the steps of: providing an oscillating head, theoscillating head having a top located feature for removably holding asurgical sagittal saw blade the head; a longitudinal axis that extendstop-to-bottom through the head; and elongated trunk that extends alongthe longitudinal axis, the elongated trunk being formed with at leastone tapered surface such that extending along the tapered surface fromthe a bottom of the tapered surface to a top of the tapered surface, thedistance between the longitudinal axis of the head and the taperedsurface changes; providing a yoke, the yoke having: features forengaging a drive shaft capable of oscillating the yoke; and a bore, thebore shaped to receive the trunk of the oscillating head, the bore beingdefined by at least one yoke tapered surface that is complementary tothe tapered surface of the yoke trunk; mounting the oscillating head tothe yoke so the trunk of the oscillating head is seated in the bore ofthe yoke such that the tapered surface of the trunk of the oscillatinghead abuts a tapered surface of the yoke; compressing the oscillatinghead and the yoke together so the tapered surface of the trunk of theoscillating head presses against the tapered surface of the yoke so theoscillating head and the yoke become a single unit; and mounting theoscillating head and attached yoke to a saw body that includes a driveshaft so that yoke engages the drive shaft and the oscillating head isable to oscillate so that the actuation of the yoke by the drive shaftresults in the back and forth oscillations of the oscillating headaround the longitudinal axis of the head.
 22. The method of assembling asurgical sagittal saw of claim 21, wherein, in said step of providing anoscillating head, an oscillating head is provided that includes a planartop surface.
 23. The method of assembling a surgical sagittal saw, ofclaim 21, wherein, in said step of providing an oscillating head, anoscillating head is provided that includes: a planar top surface; and atleast one drive pin that extends upwardly from the top surface, thedrive pin shaped to receive a drive component of the surgical saw bladeattached to the surgical sagittal saw.
 24. The method of assembling asurgical sagittal saw of claim 21, wherein, in said step of mounting theoscillating head and yoke to the saw body, at least one bearing ispositioned between the oscillating head and the saw body is used torotatably hold oscillating head to the saw body.
 25. The method ofassembling a surgical sagittal saw of claim 21, wherein: in said step ofmounting the oscillating head and yoke to the saw body, a first bearingis positioned laced between the top of oscillating head and the yoke soas to extend between the oscillating head and the saw body and a secondbearing is placed between the yoke and a bottom of the oscillating headso as to extend between the oscillating head and the saw body so thatthe first and second bearings rotatably hold the oscillating head to thesaw body.
 26. The method of assembling a surgical sagittal saw of claim21, wherein, in said step of compressing the oscillating head and theyoke together, a fastener is disposed over the oscillating head adjacentthe trunk and urged against the yoke to press the yoke against theoscillating head.
 27. The method of assembling a surgical sagittal sawof claim 21, wherein: in said step of providing an oscillating head, anoscillating head is provided that has a trunk with a plurality oftapered surfaces; in said step of providing a yoke, a yoke is providedthat has a plurality of tapered surfaces such that the tapered surfacesof the yoke are complementary to the tapered surfaces of the trunk ofthe oscillating head; in said step of mounting the oscillating head andthe yoke together, the oscillating head is seated in the bore of theyoke so that each tapered surface of the trunk of the oscillating headabuts a tapered surface of yoke so that in said step of compressing theoscillating head and the yoke together, each tapered surface of thetrunk of the oscillating head presses against a tapered surface of theyoke.
 28. The method of assembling a surgical sagittal saw of claim 21,wherein in said step of mounting the oscillating head and attached yoketo a saw body, the oscillating head and attached yoke are mounted to asaw body that includes a coupling member for releasably holding a bar ofthe saw blade static to the saw body.
 29. The method of assembling asurgical sagittal saw of claim 21, wherein: in said step of providing anoscillating head, an oscillating head is provided that includes: aplanar top surface; and at least one drive pin that extends upwardlyfrom the top surface, the drive pin shaped to receive a drive componentof the surgical saw blade attached to the surgical sagittal saw; and insaid step of mounting the oscillating head and attached yoke to a sawbody, the oscillating head and attached yoke are mounted to a saw bodythat includes a coupling member for holding a bar of the saw bladestatic to the saw body, the bar being separate from the drive componentof the surgical saw blade.
 30. A surgical sagittal saw for actuating asurgical sagittal saw blade, said saw being manufactured according tothe steps of: providing an oscillating head, the oscillating head havinga top located feature for removably holding a surgical sagittal sawblade the head; a longitudinal axis that extends top-to-bottom throughthe head; and elongated trunk that extends along the longitudinal axis,the elongated trunk being formed with at least one tapered surface suchthat extending along the tapered surface from the a bottom of thetapered surface to a top of the tapered surface, the distance betweenthe longitudinal axis of the head and the tapered surface changes;providing a yoke, the yoke having: features for engaging a drive shaftcapable of oscillating the yoke; and a bore, the bore shaped to receivethe trunk of the oscillating head, the bore being defined by at leastone yoke tapered surface that is complementary to the tapered surface ofthe yoke trunk; mounting the oscillating head to the yoke so the trunkof the oscillating head is seated in the bore of the yoke such that thetapered surface of the trunk of the oscillating head abuts a taperedsurface of the yoke; compressing the oscillating head and the yoketogether so the tapered surface of the trunk of the oscillating headpresses against the tapered surface of the yoke so the oscillating headand the yoke become a single unit; and mounting the oscillating head andyoke to a saw body that includes a drive shaft so that yoke engages thedrive shaft and the oscillating head is able to oscillate so that theactuation of the yoke by the drive shaft results in the back and forthoscillations of the oscillating head around the longitudinal axis of thehead.
 31. The surgical sagittal saw manufactured according to the methodof claim 30, wherein, in said step of providing an oscillating head, anoscillating head is provided that includes a planar top surface.
 32. Thesurgical sagittal saw manufactured according to the method of claim 30,wherein, in said step of providing an oscillating head, an oscillatinghead is provided that includes: a planar top surface; and at least onedrive pin that extends upwardly from the top surface, the drive pinshaped to receive a drive component of the surgical saw blade attachedto the surgical sagittal saw.
 33. The surgical sagittal saw manufacturedaccording to the method of claim 30, wherein, in said step of mountingthe oscillating head and yoke to the saw body, at least one bearing ispositioned between the oscillating head and the saw body is used torotatably hold oscillating head to the saw body.
 34. The surgicalsagittal saw manufactured according to the method of claim 30, wherein:in said step of mounting the oscillating head and yoke to the saw body,a first bearing is positioned laced between the top of oscillating headand the yoke so as to extend between the oscillating head and the sawbody and a second bearing is placed between the yoke and a bottom of theoscillating head so as to extend between the oscillating head and thesaw body so that the first and second bearings rotatably hold theoscillating head to the saw body.
 35. The surgical sagittal sawmanufactured according to the method of claim 30, wherein, in said stepof compressing the oscillating head and the yoke together, a fastener isdisposed over the oscillating head and urged against the yoke to pressthe yoke against the oscillating head.
 36. The surgical sagittal sawmanufactured according to the method of claim 30, wherein: in said stepof providing an oscillating head, an oscillating head is provided thathas a trunk with a plurality of tapered surfaces; in said step ofproviding a yoke, a yoke is provided that has a plurality of taperedsurfaces such that the tapered surfaces of the yoke are complementary tothe tapered surfaces of the trunk of the oscillating head; in said stepof mounting the oscillating head and the yoke together, the oscillatinghead is seated in the bore of the yoke so that each tapered surface ofthe trunk of the oscillating head abuts a tapered surface of yoke sothat in said step of compressing the oscillating head and the yoketogether, each tapered surface of the trunk of the oscillating headpresses against a tapered surface of the yoke.
 37. The surgical sagittalsaw manufactured according to the method of claim 30, wherein in saidstep of mounting the oscillating head and attached yoke to a saw body,the oscillating head and attached yoke are mounted to a saw body thatincludes a coupling member for releasably holding a bar of the saw bladestatic to the saw body.
 38. The surgical sagittal saw manufacturedaccording to the method of claim 30, wherein: in said step of providingan oscillating head, an oscillating head is provided that includes: aplanar top surface; and at least one drive pin that extends upwardlyfrom the top surface, the drive pin shaped to receive a drive componentof the surgical saw blade attached to the surgical sagittal saw; and insaid step of mounting the oscillating head and attached yoke to a sawbody, the oscillating head and attached yoke are mounted to a saw bodythat includes a coupling member for holding a bar of the saw bladestatic to the saw body, the bar being separate from the drive componentof the surgical saw blade.